Surface anchored light chain bait antibody display system

ABSTRACT

The present invention provides, in part, an antibody display system that simultaneously uses a secretion and a display mode. Embodiments of the invention provide a system in which a bait complexed with a monovalent antibody fragment can be captured prior to secretion in a host cell by virtue of surface displaying an antibody light chain and utilizing the covalent interaction of this light chain with the heavy chain of an antibody molecule that is co-expressed in the same host. Polypeptides, polynucleotides and host cells useful for making the antibody display system are also provided along with methods of using the system for identifying antibodies that bind specifically to an antigen of interest.

This application claims the benefit of U.S. Provisional Patent Application No. 61/645,763, filed May 11, 2012, which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The field of the invention relates to antibody display systems and methods of use for identifying antibodies that bind specifically to an antigen.

BACKGROUND OF THE INVENTION

Phage display is a well-known technique for constructing and screening antibody libraries, whereby the protein of interest is expressed as a polypeptide fusion to a bacteriophage coat protein and subsequently screened by binding to immobilized or soluble biotinylated ligand. Traditional phage display, however, has several shortcomings. For example, some eukaryotic secreted proteins and cell surface proteins require post-translational modifications such as glycosylation or extensive disulfide isomerization, which are unavailable in bacterial cells.

Current yeast surface antibody display systems, such as cold capture, also suffer from various drawbacks. In the cold capture antibody display system, at low temperatures, the process of antibody release from host cell transport vesicles is delayed, so that the secreted antibody can be assayed on the cell surface for antigen binding. The cold capture method suffers from a low signal-to-noise ratio and identification of an antibody with specificity for the target antigen depends heavily on cellular expression levels of the antibody.

The affinity matrix system couples antibodies to the host cell surface, e.g., by biotin, where they can be assayed for antigen binding. The affinity matrix system exhibits a high incidence of cross-contamination between antibody clones. Antibodies may become decoupled from the host cell and, thus lose their link to the polynucleotides encoding their immunoglobulin chains.

Full length antibody display systems tether the full length antibody on the host cell surface by binding an immunoglobulin binding protein, such as protein A, that is fused to a cell surface anchor protein. The host cell contains polynucleotides encoding the antibody immunoglobulin chains. Typically, binding of the antibody occurs after the immunoglobulin binding protein is expressed on the cell surface. This system, thus, leads to some erroneous binding of the antibody to host cells that do not express the antibody. The present system and methods provide numerous advantages over these earlier methods.

SUMMARY OF THE INVENTION

The present invention provides, in part, an antibody display system that does not suffer from shortcomings of currently available systems. This display system allows for the discovery of novel Fc variants that possess specific desired biological properties, such as Fc receptor binding affinities. It also allows for engineering of the Fab region. Previous methods relied on capturing antibodies on the cell surface following secretion in culture medium. Methods and capture systems of the present invention avoid cross-contamination between clones within the same culture by capturing the antibody prior to secretion. Advantageously, embodiments of the present invention allow co-secretion of the displayed molecule allowing further in vitro analysis.

The present invention provides an antibody display system comprising:

-   -   (a) an isolated host cell;     -   (b) a bait comprising a light immunoglobulin chain or functional         fragment thereof fused to a surface anchor polypeptide or         functional fragment thereof;     -   (c) one or more polynucleotides encoding an immunoglobulin light         chain variable region; and     -   (d) one or more polynucleotides encoding an immunoglobulin heavy         chain variable region.

Optionally, the antibody display system further comprises:

-   -   (i) a non-tethered full antibody or antigen-binding fragment         thereof comprising said immunoglobulin light and heavy chains         encoded by said polynucleotides; and/or     -   (ii) a monovalent antibody fragment which is complexed with an         immunoglobulin heavy chain which is complexed with the         immunoglobulin light chain of the bait.

In an embodiment of the invention, said one or more polynucleotides encoding an immunoglobulin light chain is from a genetically diverse population of immunoglobulin light chains; and/or, said one or more polynucleotides encoding an immunoglobulin heavy chain is from a genetically diverse population of immunoglobulin heavy chains.

In yet an additional embodiment of the invention, the host cell comprises a polynucleotide encoding the bait which is operably associated with a regulatable promoter.

In certain embodiments, the host cell is a Pichia cell or a Saccharomyces cerevisiae cell.

The present invention also provides an isolated bait polypeptide comprising a light immunoglobulin chain or functional fragment thereof fused, optionally by a peptide linker, to a surface anchor polypeptide or a functional fragment thereof; which bait polypeptide is optionally amino-terminally fused to a signal peptide. The bait polypeptide includes the surface anchor polypeptide is SED-1 or a functional fragment thereof. In certain embodiments, the light immunoglobulin chain or functional fragment thereof comprises a kappa or lambda constant immunoglobulin domain.

Any isolated polynucleotide encoding any of the polypeptides; vectors including the polynucleotides and isolated host cells comprising the polynucleotides and vectors are encompassed by the present invention. Additionally, the present invention includes an isolated host cell (e.g., a eukaryotic host cell (including Chinese hamster ovary cells, i.e., CHO cells), also including a lower eukaryotic yeast or filamentous fungi host cell, such as a Pichia, e.g., Pichia pastoris cell) further comprising one or more polynucleotides encoding an immunoglobulin light chain; and/or one or more polynucleotides encoding an immunoglobulin heavy chain. In certain embodiments, the bait polypeptide is located on the surface of the cell membrane.

The present invention also provides a composition comprising the host cell of any one of the present invention (see e.g., above), further comprising a non-tethered full antibody or antigen-binding fragment thereof comprising said immunoglobulin light and heavy chains; and/or a bait/antigen-binding fragment or bait/antibody; optionally, complexed with an antigen.

The present invention also provides a method for determining if an antibody or antigen-binding fragment thereof, secreted from a host cell, specifically binds to an antigen comprising contacting an antibody display system with said antigen; wherein the antibody display system comprises:

-   -   (a) an isolated eukaryotic host cell (e.g., Pichia such as         Pichia pastoris) comprising one or more polynucleotides encoding         an immunoglobulin light chain; and one or more polynucleotides         encoding an immunoglobulin heavy chain that complexes with the         light immunoglobulin chain or a functional fragment thereof of a         bait; and     -   (b) a bait comprising a light immunoglobulin chain or functional         fragment thereof fused to a surface anchor polypeptide or         functional fragment thereof (e.g., SED1);     -   and determining if a bait/antigen-binding fragment or         bait/antibody comprising said bait and heavy and light chain         immunoglobulins specifically binds, at the cell surface, to said         antigen;     -   wherein the secreted antibody or antigen-binding fragment         thereof is determined to specifically bind said antigen if said         bait/antigen-binding fragment or bait/antibody specifically         binds, at the cell surface, to said antigen.

In an embodiment of the invention, the method further comprises isolating the identified polynucleotides. In an embodiment of the invention, the method further comprises inhibiting expression of said bait, and determining the affinity of said secreted antibody or antigen-binding fragment thereof for said antigen.

In yet an additional embodiment of the invention, the method further comprises recombinantly expressing the immunoglobulin chains encoded by the polynucleotides and, optionally, isolating an antibody or antigen-binding fragment thereof comprising said immunoglobulins and, optionally, producing a pharmaceutical formulation comprising combining said antibody or antigen-binding fragment thereof and a pharmaceutically acceptable carrier.

The present invention also provides a method for making an antibody display system comprising:

-   -   (a) providing an isolated eukaryotic host cell (e.g., Pichia         such as Pichia pastoris),     -   (b) introducing, into said host cell a bait comprising a light         chain immunoglobulin domain fused to a surface anchor         polypeptide; and         -   (i) one or more polynucleotides encoding an immunoglobulin             light chain; and         -   (ii) one or more polynucleotides encoding an immunoglobulin             heavy chain.

The present invention also provides an antibody display system that is a product of the methods described herein.

The present invention also provides an antibody display system that utilizes any glycoengineered Pichia that is capable of producing heterologous proteins with human like N-glycans, as a host.

The present invention also provides a method for making an antibody or antigen-binding fragment thereof comprising introducing, into an isolated eukaryotic host cell (e.g., Pichia such as Pichia pastoris) comprising a bait that comprises a light chain immunoglobulin or functional fragment thereof fused to a surface anchor polypeptide or functional fragment thereof, one or more polynucleotides encoding an immunoglobulin light chain; and/or one or more polynucleotides encoding an immunoglobulin heavy chain; and culturing the host cell under condition whereby the polynucleotides encoding the immunoglobulin chains are expressed and an antibody or antigen-binding fragment thereof is formed from said chains; wherein said bait is operably associated with a regulatable promoter and bait expression is inhibited when said immunoglobulin chains are expressed.

The present invention also provides a method for determining the effect of a sugar on an antibody or antigen-binding fragment thereof which specifically binds to an antigen comprising contacting an antibody display system with said antigen; wherein the antibody display system comprises:

-   -   (a) an isolated controlled glycosylation eukaryotic host cell         (e.g., Pichia such as Pichia pastoris) comprising a         polynucleotide encoding an immunoglobulin light chain; and a         polynucleotide encoding an immunoglobulin heavy chain; and     -   (b) a bait comprising a light chain immunoglobulin or functional         fragment thereof fused to a surface anchor polypeptide or         functional fragment thereof (e.g., SED1) on the surface of said         host cell;     -   wherein the light chain immunoglobulin of said bait complexes         with said immunoglobulin heavy chain and immunoglobulin light         chain on the surface of the host cell; wherein said heavy or         light chain comprises said sugar;     -   determining if said bait/antigen-binding fragment specifically         binds to said antigen;     -   determining the binding affinity of the antibody or         antigen-binding fragment thereof comprising said sugar for the         antigen; and     -   comparing the affinity of the antibody or antigen-binding         fragment thereof with affinity of an otherwise identical         antibody or antigen-binding fragment thereof which lacks said         sugar;     -   wherein the sugar is determined to increase affinity for the         antigen if the affinity of the antibody or antigen-binding         fragment thereof comprising said sugar is higher than the         affinity of the antibody or antigen-binding fragment thereof         which lacks the sugar, and/or wherein the sugar is determined to         decrease affinity for the antigen if the affinity of antibody or         antigen-binding fragment thereof comprising said sugar is lower         than the affinity of the antibody or antigen-binding fragment         thereof which lacks the sugar.

The present invention also provides a method for determining the whether an mutation in an immunoglobulin heavy chain Fc region increases or decreases binding of said chain to an Fc receptor (e.g., FcγRI (CD64), FcγRIIA (CD32), FcγRIIB (CD32), FcγRIIIA (CD16a), FcγRIIIB (CD16b).) or to a lectin (e.g., DC-SIGN (CD209) and mouse ortholog SIGN-R, DCIR (dendritic cells inhibitory receptor)) comprising contacting an antibody display system with said Fc receptor or lectin; wherein the antibody display system comprises: (a) an isolated eukaryotic host cell (e.g., Pichia such as Pichia pastoris) comprising a polynucleotide encoding an immunoglobulin light chain; and a polynucleotide encoding an immunoglobulin heavy chain which comprises the mutation(s); and (b) a bait comprising a light chain immunoglobulin or functional fragment thereof fused to a surface anchor polypeptide (e.g., SED1) or functional fragment thereof on the surface of said eukaryotic host cell; wherein the light chain immunoglobulin of said bait complexes with the heavy chain immunoglobulin, to form a bait/antigen-binding fragment or bait/antibody complex, on the surface of the host cell; and determining if said bait/antigen-binding fragment or bait/antibody specifically binds to said Fc receptor or lectin; and determining the binding affinity of the antibody or antigen-binding fragment thereof for the Fc receptor or lectin; and comparing the affinity of the antibody or antigen-binding fragment thereof with affinity of an otherwise identical antibody or antigen-binding fragment thereof which lacks said mutation; wherein the mutation is determined to increase affinity of the heavy chain for the Fc receptor or lectin if the affinity of the antibody or antigen-binding fragment thereof comprising said mutation is higher than the affinity of the antibody or antigen-binding fragment thereof which lacks the mutation, and/or wherein the mutation is determined to decrease affinity for the Fc receptor or lectin if the affinity of antibody or antigen-binding fragment thereof comprising said mutation is lower than the affinity of the antibody or antigen-binding fragment thereof which lacks the mutation.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: Plasmid map of pGLY11714 containing anti-PCSK9 Lc bait cassette.

FIG. 2: A schematic representation of the Lc-Sed1p antibody display system. The DNA sequence comprising the IgG light chain (Lc) is fused through a flexible linker to a cell wall anchoring partner, in this case the S. cerevisiae GPI anchor Sed1p is used. When co-expressed in the same host with a secretable full length IgG molecule, the Lc portion of the anchored fusion (the bait) heterodimerizes in the ER with the heavy chain (Hc) region of the IgG molecule, forming disulfide bridges. Since the surface displayed half IgG molecule can still pair with secreted heavy and light chains (H+L), this complex results in surface display of the full length IgG molecule (two heavy chains paired with two light chains, i.e., H2+L2). Meanwhile the assembly of soluble full length IgG occurs with equal probability resulting in secretion of the bivalent (H2+L2) in the culture medium.

FIGS. 3A-D: FACS analysis of glycoengineered yeast expressing human IgGs and the Lc-SED1 bait expression cassette. The engineered cell cultures were induced by incubation BMMY with PMTi inhibitor. Cells were labeled with APC 635 labeled mouse anti-Human Fc, and His tagged: Hs FcγRI, Hs FcγRIIB, or Mm FcγRIIB followed by DyeLight 488 labeled anti-His and assayed by flow cytometry to detect Fc binding of displayed IgGs. FIG. 3A shows parental anti-Her2 strain without Lc-Sed1p bait. FIG. 3B shows an anti Her2 IgG1 strain containing the Lc-Sed1p bait. FIG. 3C shows Lc-Sed1p co-expressed with anti-PCSK9 IgG2 that harbors a mutation in the Fc region (F243A/V264A). FIG. 3D shows Lc-Sed1p co-expressed with anti-PCSK9 IgG2 that harbors a mutation in the Fc region F243A/V264A/S267E/L328F.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and system for antibody surface display that simultaneously features a display mode and full antibody secretion mode. Host cells secrete full antibody or antigen-binding fragment thereof (e.g., Fab, Fab′, F(ab′)₂ or single chain antibody) and display bait/antigen-binding fragments or bait/antibodies on the cell surface. This method utilizes a light immunoglobulin chain (e.g., VL-CL; e.g., human) fusion (e.g., fused at the N- or C-terminus) with a cell surface protein, such as SED-1, as “bait” that is covalently coupled to the cell surface (e.g., the cell wall), on, or embedded (partially or fully) in the cell membrane (e.g., as a transmembrane protein) and that is co-expressed with immunoglobulin chains of an antibody or antigen-binding fragment thereof (e.g., a single specific antibody or fragment from a clonal source or from a library). In an embodiment of the invention, in the endoplasmic reticulum, where antibody molecules normally dimerize to form a full antibody molecule, the light chain immunoglobulin of the bait heterodimerizes with a heavy chain of said antibody or antigen-binding fragment thereof (e.g., forming a monovalent antibody fragment) which complex is displayed on the cell surface. Light/heavy chain complexes, such as monovalent antibody fragments, on the cell surface, can bind antigen.

While not wishing to be bound by theory, embodiments of the present invention operate by surface displaying an antibody light chain and utilizing the covalent interaction of this light chain with the heavy chain of an antibody molecule that is co-expressed in the same host. This interaction tethers the IgG molecule on the cell surface (See FIG. 2). This display allows for the discovery of novel Fc variants that possess specific desired biological properties, such as Fc receptor binding affinities. It also allows for engineering of the Fab region. Previous methods relied on capturing antibodies on the cell surface following secretion in culture medium. Methods and capture systems of the present invention avoid cross-contamination between clones within the same culture by capturing the antibody prior to secretion. Advantageously, embodiments of the present invention allow co-secretion of the displayed molecule allowing further in vitro analysis.

A complex between the bait (e.g., the light chain immunoglobulin of the bait) and a heavy chain immunoglobulin may be referred to as a “bait/antigen-binding fragment”.

In an embodiment of the invention, the antibody display system of the present invention and methods of making or using such a system specifically excludes embodiments wherein the bait comprises any heavy immunoglobulin chains or fragments thereof that are fused to the cell surface protein, e.g., Hc-Sed1p.

The antibody system of the present invention can be employed in any host cell (e.g., yeast, mammalian cells, bacteria) wherein a bait can be expressed at the host cell surface and, for example, wherein the bait/antigen-binding fragment or bait/antibody can bind to an antigen while on the cell surface.

In an embodiment of the invention, formation of antibody or antigen-binding fragment thereof, free of bait, still occurs allowing secretion of the antibody or fragment into the culture supernatant. The secreted antibody or fragment can be used, e.g., for preclinical studies, e.g., after isolation.

If desired, bait can be knocked-out or mutated or its expression can be turned off to create a strain producing only the antibody or fragment (free of bait).

Molecular Biology

In accordance with the present invention there may be employed conventional molecular biology, microbiology, and recombinant DNA techniques within the skill of the art. Such techniques are explained fully in the literature. See, e.g., Sambrook, Fritsch & Maniatis, Molecular Cloning: A Laboratory Manual, Second Edition (1989) Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (herein “Sambrook, et al., 1989”); DNA Cloning: A Practical Approach, Volumes I and II (D. N. Glover ed. 1985); Oligonucleotide Synthesis (M. J. Gait ed. 1984); Nucleic Acid Hybridization (B. D. Hames & S. J. Higgins eds. (1985)); Transcription And Translation (B. D. Hames & S. J. Higgins, eds. (1984)); Animal Cell Culture (R. I. Freshney, ed. (1986)); Immobilized Cells And Enzymes (IRL Press, (1986)); B. Perbal, A Practical Guide To Molecular Cloning (1984); F. M. Ausubel, et al. (eds.), Current Protocols in Molecular Biology, John Wiley & Sons, Inc. (1994).

A library is, in general, a collection of related but diverse polynucleotides that are, in general, in a common vector backbone. For example, a light chain or heavy chain immunoglobulin library may contain polynucleotides, in a common vector backbone, that encode light and/or heavy chain immunoglobulins which are diverse but related in their nucleotide sequence; for example, which immunoglobulins are functionally diverse in their abilities to form complexes with other immunoglobulins, e.g., in an antibody display system of the present invention, and bind a particular antigen. For example, the polynucleotide inserts in the common vector backbone may differ by only one or two or several nucleotides, exhibiting, e.g., 90% or more sequence identity (e.g., 95 or 99%). The library may encode immunoglobulins that form full antibodies or antigen-binding fragments thereof (e.g., Fab, Fab′, F(ab′)₂ or single chain antibody).

A coding sequence is “under the control of”, “functionally associated with” or “operably associated with” transcriptional and/or translational control sequences in a cell when the sequences direct RNA polymerase mediated transcription of the coding sequence into RNA, preferably mRNA, which then may be spliced (if it contains introns) and translated into a protein encoded by the coding sequence. Thus, a polynucleotide encoding the bait can be operably associated with a promoter, such as a regulatable promoter or a constitutive promoter.

Polynucleotides discussed herein form part of the present invention. A “polynucleotide”, “nucleic acid” or “nucleic acid molecule” includes DNA and RNA, single or double stranded.

Polynucleotides e.g., encoding an immunoglobulin chain or component of the antibody display system of the present invention (e.g., a bait), may, in an embodiment of the invention, be flanked by natural regulatory (expression control) sequences, or may be associated with heterologous sequences, including, e.g., promoters, internal ribosome entry sites (IRES) and other ribosome binding site sequences, enhancers, response elements, suppressors, signal sequences, polyadenylation sequences, introns, 5′- and 3′-non-coding regions, and the like.

Polynucleotides e.g., encoding an immunoglobulin chain or component of the antibody display system of the present invention, may be operably associated with a promoter. A “promoter” or “promoter sequence” is, in an embodiment of the invention, a DNA regulatory region capable of binding an RNA polymerase in a cell (e.g., directly or through other promoter-bound proteins or substances) and initiating transcription of a coding sequence. A promoter sequence is, in general, bounded at its 3′ terminus by the transcription initiation site and extends upstream (5′ direction) to include the minimum number of bases or elements necessary to initiate transcription at any level. Within the promoter sequence may be found a transcription initiation site (conveniently defined, for example, by mapping with nuclease S1), as well as protein binding domains (consensus sequences) responsible for the binding of RNA polymerase. The promoter may be operably associated with other expression control sequences, including enhancer and repressor sequences or with a nucleic acid of the invention. Promoters which may be used to control gene expression include, but are not limited to, cytomegalovirus (CMV) promoter (U.S. Pat. Nos. 5,385,839 and 5,168,062), the SV40 early promoter region (Benoist, et al., (1981) Nature 290:304-310), the promoter contained in the 3′ long terminal repeat of Rous sarcoma virus (Yamamoto, et al., (1980) Cell 22:787-797), the herpes thymidine kinase promoter (Wagner, et al., (1981) Proc. Natl. Acad. Sci. USA 78:1441-1445), the regulatory sequences of the metallothionein gene (Brinster, et al., (1982) Nature 296:39-42); prokaryotic expression vectors such as the □-lactamase promoter (Villa-Komaroff, et al., (1978) Proc. Natl. Acad. Sci. USA 75:3727-3731), or the tac promoter (DeBoer, et al., (1983) Proc. Natl. Acad. Sci. USA 80:21-25); see also “Useful proteins from recombinant bacteria” in Scientific American (1980) 242:74-94; and promoter elements from yeast or other fungi such as the Gal 4 promoter, the ADC (alcohol dehydrogenase) promoter, PGK (phosphoglycerol kinase) promoter or the alkaline phosphatase promoter.

The terms “vector”, “cloning vector” and “expression vector” include a vehicle (e.g., a plasmid) by which a DNA or RNA sequence can be introduced into a host cell, so as to transform the host and, optionally, promote expression and/or replication of the introduced sequence. Polynucleotides encoding an immunoglobulin chain or component of the antibody display system of the present invention (e.g., a bait) may, in an embodiment of the invention, be in a vector.

A host cell that may be used in a composition or method of the present invention, as is discussed herein, includes eukaryotes such as lower and higher eukaryotic cells as well as prokaryotes. Higher eukaryote cells include mammalian, insect (e.g., Spodoptera frugiperda cells), and plant cells (e.g., Protalix cells). In an embodiment of the invention, the host cell is a lower eukaryote such as a yeast or filamentous fungi cell, which, for example, is selected from the group consisting of any Pichia cell, Pichia pastoris, Pichia flnlandica, Pichia trehalophila, Pichia koclamae, Pichia membranaefaciens, Pichia minuta (Ogataea minuta, Pichia lindneri), Pichia opuntiae, Pichia thermotolerans, Pichia salictaria, Pichia guercuum, Pichia pijperi, Pichia stiptis, Pichia methanolica, Pichia, Saccharomyces cerevisiae, Saccharomyces, Hansβnula polymorpha, Kluyveromyces, Kluyveromyces lactis, Candida albicans, Aspergillus nidulans, Aspergillus niger, Aspergillus oryzae, Trichoderma reesei, Chrysosporium lucknowense, Fusarium, Fusa{acute over (η)}um gramineum, Fusarium venenatum and Neuraspora crassa. A higher eukaryotic host cell includes a mammalian host cell for example a Chinese hamster ovary (CHO) cell, a BHK cell, or an NSO cell. A prokaryotic host cell can be, for example, a bacterial cell such as Escherichia (e.g., E. coli), Enterobacter, Azotobacter, Erwinia, Bacillus, Pseudomonas, Klebsiella, Proteus, Salmonella, Serratia, Shigella, Rhizobia, Vitreoscilla, and Paracoccus. E. coli host cells include DHB4, BL21 (which are deficient in both Lon (Phillips et al. (1984) J. Bacteriol. 159: 283) and OmpT proteases), HB101, BL21 DE3, E. coli AD494, E. coli W3110 (ATCC 27,325), E. coli 294 (ATCC 31,446), E. coli B, and E. coli X1776 (ATCC 31,537). Other strains include E. coli B834 which are methionine deficient (Leahy et al. (1992) Science 258, 987); other strains include the BLR strain, and the K-12 strains HMS174 and NovaBlue, which are recA-derivative that improve plasmid monomer yields and may help stabilize target plasmids containing repetitive sequences (these strains can be obtained from Novagen). See also U.S. Pat. Nos. 4,952,496, 5,693,489 and 5,869,320 and in Davanloo, P., et al., (1984) Proc. Natl. Acad. Sci. USA 81, 2035-2039; Studier, F. W., et al., (1986) J. Mol. Biol. 189: 113-130; Rosenberg, A. H., et al., (1987) Gene 56: 125-135; and Dunn, J. J., et al., (1988) Gene 68: 259. Prokaryotic cells can also be cultured, for example, in a medium under conditions allowing for recombinant expression of a polypeptide, such as an immunoglobulin polypeptide and/or a bait. Such methods and host cells comprising such genes and proteins are part of the present invention. A prokaryotic host cell can also be used as a host cell in the antibody display system of the present invention, as discussed herein.

As used herein, the terms “N-glycan” and “glycoform” are used interchangeably and refer to an N-linked oligosaccharide, e.g., one that is attached by an asparagine-N-acetylglucosamine linkage to an asparagine residue of a polypeptide. N-linked glycoproteins contain an N-acetylglucosamine residue linked to the amide nitrogen of an asparagine residue in the protein. Predominant sugars found on glycoproteins are glucose, galactose, mannose, fucose, N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc) and sialic acid (e.g., N-acetyl-neuraminic acid (NANA)).

N-glycans have a common pentasaccharide core of Man₃GlcNAc₂ (“Man” refers to mannose; “Glc” refers to glucose; and “NAc” refers to N-acetyl; GIcNAc refers to N-acetylglucosamine). N-glycans differ with respect to the number of branches (antennae) comprising peripheral sugars (e.g., GlcNAc, galactose, fucose and sialic acid) that are added to the Man₃GlcNAc₂ (“Man₃”) core structure which is also referred to as the “triammnose core”, the “pentasaccharide core” or the “paucimannose core”. N-glycans are classified according to their branched constituents (e.g., high mannose, complex or hybrid). A “high mannose” type N-glycan has five or more mannose residues. A “complex” type N-glycan typically has at least one GlcNAc attached to the 1,3 mannose arm and at least one GlcNAc attached to the 1,6 mannose arm of a “trimannose” core. Complex N-glycans may also have galactose (“Gal”) or N-acetylgalactosamine (“GalNAc”) residues that are optionally modified with sialic acid or derivatives (e.g., “NANA” or “NeuAc”, where “Neu” refers to neuraminic acid and “Ac” refers to acetyl). Complex N-glycans may also have intrachain substitutions comprising “bisecting” GlcNAc and core fucose (“Fuc”). Complex N-glycans may also have multiple antennae on the “trimannose core,” often referred to as “multiple antennary glycans.” A “hybrid” N-glycan has at least one GlcNAc on the terminal of the 1,3 mannose arm of the trimannose core and zero or more mannoses on the 1,6 mannose arm of the trimannose core. The various N-glycans are also referred to as “glycoforms.” “PNGase”, or “glycanase” or “glucosidase” refer to peptide N-glycosidase F (EC 3.2.2.18).

In an embodiment of the invention, O-glycosylation of glycoproteins in a “eukaryotic host cell” is controlled. The scope of the present invention includes isolated eukaryotic host cells (e.g., Pichia pastoris) wherein O-glycosylation is controlled (as discussed herein) as well as antibody display systems comprising such eukaryotic host cells and methods of use thereof (as discussed herein). For example, wherein O-glycan occupancy and mannose chain length are reduced. In lower eukaryote host cells such as yeast, O-glycosylation can be controlled by deleting the genes encoding one or more protein O-mannosyltransferases (Dol-PMan: Protein (Ser/Thr) Mannosyl Transferase genes) (PMTs) or by growing the host in a medium containing one or more Pmtp inhibitors. Thus, the present invention includes isolated eukaryotic host cells, antibody display systems and methods of use thereof (as is discussed herein), e.g., comprising a deletion of one or more of the genes encoding PMTs, and/or, e.g., wherein the host cell can be cultivated in a medium that includes one or more Pmtp inhibitors. Pmtp inhibitors include but are not limited to a benzylidene thiazolidinedione. Examples of benzylidene thiazolidinediones are 5-[[3,4bis(phenylmethoxy)phenyl]methylene]-4-oxo-2-thioxo-3-thiazolidineacetic Acid; 5-[[3-(1-25 Phenylethoxy)-4-(2-phenylethoxy)]phenyl]methylene]-4-oxo-2-thioxo-3-thiazolidineacetic Acid; and 5-[[3-(1-Phenyl-2-hydroxy)ethoxy)-4-(2-phenylethoxy)]phenyl]methylene]-4-oxo-2-thioxo3-thiazolidineacetic acid.

In an embodiment of the invention, a “eukaryotic host cell” includes a nucleic acid that encodes an alpha-1,2-mannosidase that has a signal peptide that directs it for secretion. For example, in an embodiment of the invention, the host cell is engineered to express an exogenous alpha-1,2-mannosidase enzyme having an optimal pH between 5.1 and 8.0, preferably between 5.9 and 7.5. In an embodiment of the invention, the exogenous enzyme is targeted to the endoplasmic reticulum or Golgi apparatus of the host cell, where it trims N-glycans such as Man₈GlcNAc₂ to yield Man_(s)GlcNAc₂. See U.S. Pat. No. 7,029,872.

“Eukaryotic host cells” are, in an embodiment of the invention, lower eukaryote cells (e.g., yeast such as Pichia pastoris) that are genetically engineered to eliminate glycoproteins having alpha-mannosidase-resistant N-glycans by deleting or disrupting one or more of the beta-mannosyltransferasegenes (e.g., BMT1, BMT2, BMT3, and BMT4)(See, U.S. Published Patent Application No. 2006/0211085) or abrogating translation of RNAs encoding one or more of the beta-mannosyltransferases using interfering RNA, antisense RNA, or the like. The scope of the present invention includes such an isolated eukaryotic host cell (e.g., Pichia pastoris) as well as antibody display systems comprising such eukaryotic host cells and methods of use thereof (as discussed herein).

“Eukaryotic host cells” also include lower eukaryote cells (e.g., yeast and filamentous fungi such as Pichia pastoris) that are genetically engineered to eliminate glycoproteins having phosphomannose residues, e.g., by deleting or disrupting one or both of the phosphomannosyl transferase genes PNO1 and MNN4B (See for example, U.S. Pat. Nos. 7,198,921 and 7,259,007), which can include deleting or disrupting the MNN4A gene or abrogating translation of RNAs encoding one or more of the phosphomannosyltransferases using interfering RNA, antisense RNA, or the like. In an embodiment of the invention, a “eukaryotic host cell” has been genetically modified to produce glycoproteins that have predominantly an N-glycan selected from the group consisting of complex N-glycans (sialylated α2,3 or α2,6 linkages; or asialylated), hybrid N-glycans, and high mannose N-glycans wherein complex N-glycans are, in an embodiment of the invention, selected from the group consisting of Man₃GlcNAc₂, GlcNAc₍₁₋₄₎Man₃GlcNAc₂, Gal₍₁₋₄₎GlcNAc₍₁₋₄₎Man₃GlcNAc₂, and NANA₍₁₋₄₎Gal₍₁₋₄₎Man₃GlcNAc₂; NAGNA₍₁₋₄₎Gal₍₁₋₄₎Man₃GlcNAc₂; hybrid N-glycans are, in an embodiment of the invention, selected from the group consisting of Man₅GlcNAc₂, GlcNAcMan₅GlcNAc₂, GalGlcNAcMan₅GlcNAc₂, and NANAGalGlcNAcMan₅GlcNAc₂; NAGNAGalGlcNAcMan₅GlcNAc₂ and high mannose N-glycans are, in an embodiment of the invention, selected from the group consisting of Man₆GlcNAc₂, Man₇GlcNAc₂, Mang₈1cNAc₂, and Man₉GlcNAc₂. The scope of the present invention includes such an isolated eukaryotic host cell (e.g., Pichia pastoris) as well as antibody display systems comprising such eukaryotic host cells and methods of use thereof (as discussed herein).

As used herein, the term “essentially free of” as it relates to lack of a particular sugar residue, such as fucose, or galactose or the like, on a glycoprotein, is used to indicate that the glycoprotein composition is substantially devoid of N-glycans which contain such residues. Expressed in terms of purity, essentially free means that the amount of N-glycan structures containing such sugar residues does not exceed 10%, and preferably is below 5%, more preferably below 1%, most preferably below 0.5%, wherein the percentages are by weight or by mole percent.

As used herein, a glycoprotein composition “lacks” or “is lacking” a particular sugar residue, such as fucose or galactose, when no detectable amount of such sugar residue is present on the N-glycan structures. For example, in preferred embodiments of the present invention, the glycoprotein compositions are produced by lower eukaryotic organisms, as discussed herein, and will “lack fucose,” because the cells of these organisms do not have the enzymes needed to produce fucosylated N-glycan structures. Thus, the term “essentially free of fucose” encompasses the term “lacking fucose.” However, a composition may be “essentially free of fucose” even if the composition at one time contained fucosylated N-glycan structures or contains limited, but detectable amounts of fucosylated N-glycan structures as described above.

For example, a host cell which introduces, eliminates or modifies sugar residues on an immunoglobulin expressed in the host cell, e.g., as is discussed herein, may, in certain instances, be referred to herein as a “controlled glycosylation host cell.”

The scope of the present invention includes isolated eukaryotic host cells (e.g., Pichia pastoris), e.g., any of those discussed herein, comprising an antibody display system of the present invention or any component thereof (e.g., a bait and/or polynucleotide(s) encoding a bait; and/or an immunoglobulin chain and/or polynucleotide(s) encoding the immunoglobulin chain); as well as antibody display systems comprising such eukaryotic host cells and methods of use thereof (as discussed herein).

Fluorescence-activated cell sorting (FACS) is a specialized type of flow cytometry. It provides a method for sorting a heterogeneous mixture of biological cells into two or more containers, one cell at a time, based upon the specific light scattering and fluorescent characteristics of each cell. The present invention encompasses methods of using the antibody display system of the present invention, e.g., as discussed herein, wherein the eukaryotic host cells that are bound to an antigen of interest (by the bait/antigen-binding fragment or bait/antibody) are sorted from unbound cells or cells without sufficient levels of binding, by FACS sorting. FACS sorting can, in an embodiment of the invention, be based on whether the cells are labeled with a detectable fluorescent label (e.g., wherein the antigen itself or a secondary antibody is labeled). For example, cells displaying a bait/antibody or bait/antigen-binding fragment that bind an antigen of interest can be identified based on binding of a fluorescently labeled antigen to the bait/antibody or bait/antigen-binding fragment; or based on binding of a fluorescently labeled secondary antibody to the antigen that is bound to the bait/antibody or bait/antigen-binding fragment. Such sorted, labeled host cells and compositions comprising such sorted labeled host cells are also part of the present invention.

A regulatable promoter is a promoter whose expression can be induced or inhibited. Embodiments of the invention include the antibody display system wherein expression of the bait is controlled by a regulatable promoter as well as methods of use thereof as discussed herein. Polynucleotides encoding the bait, operably associated with a regulatable promoter also form part of the present invention along with isolated eukaryotic host cells including the polynucleotides. Examples of regulatable promoters that occur in yeast include the GUT1 promoter, GADPH promoter and the PCK1 promoter.

In an embodiment of the invention, expression of a polynucleotide (e.g., the bait) in a eukaryotic host cell (e.g., a bait) is inhibited by exposing the cells to anti-sense RNA or by RNA interference (e.g., microRNA (miRNA) or small interfering RNA (siRNA)). Embodiments of the invention include methods of using antibody display system (e.g., as discussed herein) wherein expression of the bait is inhibited by RNA interference or anti-sense RNA. Isolated eukaryotic host cells of the present invention (e.g., as discussed herein) comprising bait and further comprising an anti-sense or RNA interference molecule that inhibits bait expression are part of the present invention.

Fc receptors include, for example, FcγRI (CD64), FcγRIIA (CD32), FcγRIIB (CD32), FcγRIIIA (CD16a), and FcγRIIIB (CD16b); and Lectins include, for example, DC-SIGN (CD209) and mouse ortholog SIGN-R, and DCIR (dendritic cells inhibitory receptor).

Antibodies

Host cells of the present invention include (in addition to the bait) polynucleotides encoding heavy and light immunoglobulins that complex to form an antibody or antigen-binding fragment thereof which may be secreted from the host cell. Heavy chains encoded by a polynucleotide may complex with the light chain immunoglobulin to form a bait/antigen-binding fragment or bait/antibody that includes one or more antigen-binding sites. When on the surface of the cell, the bait/antigen-binding fragment or bait/antibody may bind to an antigen and this binding may be detected, e.g., by FACS, thus indicating that the heavy and light chains comprise binding sites with specificity for the antigen.

Antibodies or antigen-binding fragments thereof identified in connection with use of the present invention (e.g., use of the antibody display system of the present invention) may be reformatted into any suitable form. For example, CDRs from a full antibody isolated using the antibody display system can be incorporated into a different framework (e.g., a human framework) to generate an antibody or antigen-binding fragment comprising the CDRs isolated from the antibody display system of the present invention. Methods for producing chimeric, humanized and human antibodies are well known in the art. See, e.g., U.S. Pat. No. 5,530,101, issued to Queen et al., U.S. Pat. No. 5,225,539, issued to Winter et al., U.S. Pat. No. 4,816,397 issued to Boss et al. Such methods for reformatting an antibody or antigen-binding fragment or for relocating CDRs from one framework to another are conventional and well known in the art. For example, the CDRs of an antibody or antigen-binding fragment can be used to generate monoclonal antibodies, polyclonal antibodies, bispecific antibodies, chimeric antibodies, recombinant antibodies, anti-idiotypic antibodies, humanized antibodies and bispecific antibodies; or antigen-binding fragments thereof such as nanobodies, Fab, Fab′, F(ab′)₂, Fv fragments; dsFv; (dsFv)₂, ds diabodies; dsFv-dsFv′; single-chain antibody molecules, e.g., sc-Fv, sc-Fv dimers (bivalent diabodies); and bispecific diabodies.

A full antibody comprises a tetramer of subunits. Each tetramer has two identical pairs of polypeptide chains, each pair having one “light” chain (LC) and one “heavy” chain (HC). Light chains (LCs) are classified as either kappa or lambda based on the type of constant domain in the light chain. Heavy chains (HCs) are classified as gamma, mu, alpha, delta, or epsilon, based on the type of constant domain in the heavy chain, and define the antibody's isotype as IgG (e.g., IgG1, IgG2, IgG2a, IgG2b, IgG3 or IgG4), IgM, IgA (e.g., IgA1 or IgA2), IgD or IgE, respectively.

The present invention encompasses methods for making an antibody or antigen-binding fragment thereof comprising introducing, into an isolated host cell (e.g., a eukaryotic host cell such as Pichia, e.g., Pichia pastoris) comprising a bait comprising a light immunoglobulin chain (e.g., VL-CL; e.g., human) fused to a surface anchor, e.g., SED-1, or a functional fragment thereof; one or more polynucleotides encoding an immunoglobulin light chain; and/or one or more polynucleotides encoding an immunoglobulin heavy chain and culturing the host cell under condition whereby the polynucleotides encoding the immunoglobulin light and heavy chains are expressed and an antibody or antigen-binding fragment thereof is formed from said chains.

In an embodiment of the invention, said bait is operably associated with a regulatable promoter and the bait expression is inhibited when said immunoglobulin chains are expressed. In an embodiment of the invention, bait expression is inhibited with anti-sense RNA or by RNA interference.

The present invention also provides a method for determining the quantity of an antibody or antigen-binding fragment thereof, e.g., by enzyme linked immunosorbent assay (ELISA). For example, in an embodiment of the invention, the method comprises culturing a eukaryotic host cell comprising an isolated polypeptide comprising a bait polypeptide comprising a light immunoglobulin chain (e.g., VL-CL; e.g., human) fused to a surface anchor polypeptide or functional fragment thereof); wherein the host cell secretes full antibody or antigen-binding fragment thereof (optionally, the antibody or fragment is isolated from the host cell and/or culture medium); and determining the quantity of the antibody or antigen-binding fragment thereof by ELISA. In an embodiment of the invention, expression of the bait is inhibited before quantitation such that the host cell expresses and secretes only full antibody. Bait polynucleotide can be operably associated with a regulatable promoter which is inhibited so as to inhibit bait expression. For example, in an embodiment of the invention, ELISA comprises coating the antigen on a solid substrate; binding the antibody or antigen-binding fragment thereof to the antigen; binding a detectably labeled secondary antibody to the antibody or fragment; and detecting the secondary antibody. In an embodiment of the invention, the secondary antibody is labeled with alkaline phosphatase or horse radish peroxidase. In an embodiment of the invention, the label is detected by binding the alkaline phosphatase (AP) or horse radish peroxidase (HRP) with substrate and measuring absorbance of the plate (e.g., HRP substrate 3,3′,5,5′-tetramethylbenzidine (TMB); HRP substrate 3,3′-diaminobenzidine (DAB); or HRP substrate 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS); or AP substrate para-nitrophenylphosphate).

The present invention also provides a method for determining the affinity of an antibody or antigen-binding fragment thereof, that is secreted from a eukaryotic host cell in the antibody display system of the present invention, for an antigen. For example, the affinity can be determined by standard affinity ELISA, Biacore™ analysis or competition assays.

Antibody Display System

The present invention provides an antibody display system, composition or kit comprising (1) a eukaryotic host cell and (2) a bait comprising a light immunoglobulin chain (e.g., VL-CL; e.g., human) fused, at the N- or C-terminus, optionally, by a peptide linker such as GGGS (×3), to a surface anchor which bait is optionally linked to a signal sequence (e.g., an alpha mating factor signal sequence, e.g., from Saccharomyces cerevisiae); which system may be used, for example, in the identification of antibodies and antigen-binding fragments thereof that bind an antigen of interest. Thus, in an embodiment of the invention, the host cell in the system expresses one or more immunoglobulin chains (e.g., light and heavy chains, e.g., wherein one or more of the chains are from a library source) of an antibody or antigen-binding fragment thereof, and/or of a bait/antigen-binding fragment or bait/antibody.

The light chain immunoglobulin of the bait may be the same or different from the light chain immunoglobulin that is not part of the bait. A host cell may contain more than one sequence of heavy chain immunoglobulin.

A bait/antigen-binding fragment of an antibody (1) is a complex between light immunoglobulin chain of the bait (e.g., VL-CL; e.g., human) and a heavy chain immunoglobulin; and, (2) binds to an antigen when on the surface of the host cell. An example of a bait/antigen-binding fragment is a monovalent fragment of a full antibody (i.e., a monovalent antibody fragment) bound to the cell surface anchor of the bait. A bait/antibody is a complex between light immunoglobulin chain of the bait (e.g., VL-CL; e.g., human) and light and heavy chain immunoglobulins which form a full antibody tetrameric complex having two heavy and two light chains; that binds to an antigen when on the surface of the host cell.

A “monovalent antibody fragment” comprises one half of an antibody, i.e., the antibody heavy chain (VH-CH1-CH2-CH3) bound to the antibody light chain (VL-CL) comprising three paired CDRs, e.g., wherein CH1 and CL are bound by a disulfide bridge, which monovalent antibody fragment is capable of detectably binding an antigen.

The “bait” comprises a light chain immunoglobulin such as, for example, a CL polypeptide or a VL-CL polypeptide fused, e.g., at the amino-terminus or carboxy-terminus, to a cell surface anchor, which bait possesses functional properties described herein (e.g., as set forth below) that enable the bait to function in the antibody display system of the present invention. The light chain immunoglobulin of the bait can, in an embodiment of the invention, be mutated so as to improve its ability to function in the antibody display system of the present invention, for example, cysteines or other residues may be added or moved to allow for more extensive disulfide bridges to form when complexed with a heavy chain immunoglobulin. A light chain immunoglobulin suitable for use in the bait is capable of dimerizing, when fused to a surface anchor protein, with, for example, a heavy chain immunoglobulin; on the surface of a eukaryotic host cell. In an embodiment of the invention, dimerization between the bait and immunoglobulin heavy chain occurs intracellularly, prior to routing to the cell surface, wherein heavy chain immunoglobulin and the bait remain associated once at the cell surface. In an embodiment of the invention, a full antibody or antigen-binding fragment thereof that is co-expressed with the bait comprises light and heavy chains capable of dimerizing with each other to form a monovalent antibody fragment, which monovalent antibody fragment is also capable of dimerizing with a complex between the light chain of the bait and a heavy chain immunoglobulin. (See FIG. 2).

An antigen can be any immunogenic molecule or substance, for example, a polypeptide (e.g., an oligopeptide), a cell membrane, cell extract or a whole cell. Polypeptide antigens include, for example, the following polypeptides: chemokines, cytokines (e.g., inflammatory cytokines or chemokines), receptors, PCSK9, granulocyte-CSF; coagulation factors such as factor VIII, factor IX, and human protein C; soluble IgE receptor alpha-chain; urokinase; chymase and urea trypsin inhibitor; IGF-binding protein; insulin-like growth factor-1 receptor, vascular epidermal growth factor, epidermal growth factor; growth hormone-releasing factor; GITR (glucocorticoid-induced TNFR-related protein), annexin V fusion protein; IL-23p19, IL-23p40, IL-23R, IL12R-beta 1, TNF alpha (tumor necrosis factor alpha), TGF beta (transforming growth factor beta), IL-10, IL-17, TSLP (Thymic stromal lymphopoietin), angiostatin; vascular endothelial growth factor-2; myeloid progenitor inhibitory factor-1; osteoprotegerin (OPG), RANK (receptor activator for nuclear factor kappa B) or RANKL (receptor activator for nuclear factor kappa B ligand); any of which can be, in an embodiment of the invention, human.

A “surface anchor” is any polypeptide that, when fused with a light chain immunoglobulin or functional fragment thereof (e.g., VL-CL or CL or VL), is expressed and located to the cell surface and to which a heavy chain immunoglobulin can complex via binding to the light chain immunoglobulin of the bait. Examples of a suitable cell surface anchor is a protein such as, but not limited to any of the following: SED1P, α-agglutinin, Cwp1, Cwp2, GasI, Yap3, FloIp1 Crh2, Pir1, Pir4, Tip1, Wpi, Hpwpl, Als3, and Rbt5; for example, Saccharomyces cerevisiae CWP1, CWP2, SED1, or GAS1; Pichia pastoris SP1 or GAS1; or H. polymorpha TIP1; or any functional fragment or variant thereof these proteins, which are described in international publication No. WO09/111183. In an embodiment of the invention, the surface anchor is any glycosylphosphatidylinositol-anchored (GPI) protein. A functional fragment of a surface anchor comprises a fragment of a full surface anchor polypeptide that can, to some degree, function, as does a full surface anchor polypeptide, in the antibody display system of the present invention.

As discussed herein, a suitable eukaryotic host cell for use in the antibody display system of the present invention is a Pichia cell such as Pichia pastoris.

The scope of the present invention encompasses an isolated eukaryotic host cell (e.g., Pichia pastoris) comprising a bait, e.g., on the cell surface, optionally, wherein the bait is dimerized with one or more immunoglobulin chains to form a bait/antigen-binding fragment or bait/antibody. The present invention also includes a composition comprising such a eukaryotic host cell further comprising a secreted antibody or antigen-binding fragment thereof, e.g., in a liquid culture medium.

The present invention provides, for example, methods for using the antibody display system of the present invention. For example, the present invention comprises a method for identifying (i) an antibody or antigen-binding fragment thereof; or, a bait/antigen-binding fragment or bait/antibody, that binds specifically to an antigen of interest; and/or (ii) a polynucleotide encoding an immunoglobulin heavy or light polypeptide chain of any of the foregoing; or either of said immunoglobulin polypeptide chains themselves. The method comprises, in an embodiment of the invention:

(a) co-expressing a bait (e.g., comprising a polypeptide comprising light chain immunoglobulin that is linked to a cell surface anchor, such as Sed1p) and one or more heavy and light immunoglobulin chains (e.g., wherein one or more of such chains are encoded by a polynucleotide from a library source) in an isolated eukaryotic host cell (e.g., Pichia pastoris) such that a complex between the light chain immunoglobulin of the bait and one or more of said heavy chain immunoglobulins forms (e.g., a bait/antibody or bait-antigen-binding fragment), and is located at the cell surface; for example, wherein the host cell is transformed with one or more polynucleotides encoding the bait and/or the immunoglobulin chains;

(b) identifying a eukaryotic host cell expressing the bait, dimerized with the heavy chain immunoglobulin, which has detectable affinity (e.g., acceptable affinity) for the antigen (e.g., which detectably binds to the antigen);

In an embodiment of the invention, non-tethered, secreted full antibodies or antigen-binding fragments thereof comprising light and heavy chain immunoglobulins that were introduced into the host cell are formed. These may be analyzed to determine if they possess detectable affinity.

In an embodiment of the invention, the full antibodies or antigen-binding fragments thereof are secreted from the host cell into the medium. In an embodiment of the invention, the secreted full antibodies or antigen-binding fragments thereof are isolated from the host cell and/or medium.

In an embodiment of the invention, after step (b), expression of the bait in the host cell is inhibited, but expression of the full antibodies or antigen-binding fragments thereof is not inhibited. In this embodiment of the invention, the host cell expresses only the full antibody but does not express the bait at any significant quantity. Once expression of the bait is inhibited, in an embodiment of the invention, the full antibody produced from the host cell is analyzed to determine if it possesses detectable affinity (e.g., acceptable affinity); and,

(c) identifying said antibodies or antigen-binding fragments or polynucleotides if detectable binding of the bait/antigen-binding fragment or bait/antibody to antigen is observed, e.g., wherein one or more of the polynucleotides encoding the light and/or heavy chain immunoglobulin are optionally isolated from the host cell. In an embodiment of the invention, the nucleotide sequence of the polynucleotide is determined.

In an embodiment of the invention, a population of host cells express a common bait and a common immunoglobulin heavy chain as well a variety of different light chain immunoglobulins (non-bait chains), e.g., from a library source, wherein individual light chain immunoglobulins that form bait/antigen-binding fragments and full antibodies that are tethered to the bait and which exhibit antigen binding can be identified. Similarly, in an embodiment of the invention, a population of host cells express a common bait and a common immunoglobulin light chain (non-bait) as well a variety of different heavy chain immunoglobulins, e.g., from a library source, wherein individual heavy chain immunoglobulins that form bait/antigen-binding fragments and full antibodies that are tethered to the bait and which exhibit antigen binding can be identified.

In an embodiment of the invention, the host cell possessing polynucleotides encoding the heavy and light chain immunoglobulins can be further used to express the secreted non-tethered antibody (e.g., full antibody) or an antigen-binding fragment thereof in culture. For example, in this embodiment of the invention, expression of the bait is optionally inhibited so that bait expression at significant quantities does not occur. The host cell is then cultured in a culture medium under conditions whereby secreted, non-tethered antibody (e.g., full antibody) or antigen-binding fragment thereof is expressed and secreted from the host cell. The non-tethered antibody or antigen-binding fragment thereof can optionally be isolated from the host cell and culture medium. In an embodiment of the invention, the immunoglobulin chains are transferred to a separate host cell (e.g., lacking the antibody display system components) for recombinant expression.

The antibody display system of the present invention may be used to evaluate the effects of a given glycosylation pattern on the affinity of an antibody or antigen-binding fragment thereof for an antigen. In general, the ability of the bait/antigen-binding fragment or bait/antibody comprising an altered glycosylation pattern to bind antigen may be evaluated, after which affinity of free full antibody or antigen-binding fragment thereof can be evaluated. Glycosylation patterns can be modified on the immunoglobulin chains expressed in the antibody display system, for example, by using a host cell, e.g., as is discussed herein, that modifies the glycosylation patterns when the chains are expressed and/or by culturing a host under conditions whereby the glycosylation pattern is modified, e.g., as discussed herein. For example, in an embodiment of the invention, the method comprise contacting an antibody display system with said antigen; wherein the antibody display system comprises: (a) an isolated eukaryotic controlled glycosylation host cell comprising a polynucleotide encoding an immunoglobulin light chain; and a polynucleotide encoding an immunoglobulin heavy chain; and (b) a bait comprising a light chain immunoglobulin or functional fragment thereof fused to a surface anchor polypeptide or functional fragment thereof on the surface of said eukaryotic host cell; wherein the light chain immunoglobulin of said bait complexes with a heavy chain immunoglobulin, to form a bait/antigen-binding fragment or bait/antibody, on the surface of the host cell; wherein said heavy or light chain comprises said sugar; determining if said bait/antigen-binding fragment or bait/antibody specifically binds to said antigen; determining the binding affinity of the antibody or antigen-binding fragment thereof comprising said sugar for the antigen; and comparing the affinity of the antibody or antigen-binding fragment thereof with affinity of an otherwise identical antibody or antigen-binding fragment thereof which lacks said sugar; wherein the sugar is determined to increase affinity for the antigen if the affinity of the antibody or antigen-binding fragment thereof comprising said sugar is higher than the affinity of the antibody or antigen-binding fragment thereof which lacks the sugar, and/or wherein the sugar is determined to decrease affinity for the antigen if the affinity of antibody or antigen-binding fragment thereof comprising said sugar is lower than the affinity of the antibody or antigen-binding fragment thereof which lacks the sugar. For example, the affinity of the antibody or antigen-binding fragment thereof lacking the sugar can be determined in a similar manner in the antibody display system of the present invention or the affinity of it can be determined directly by measuring affinity by a known method such as ELISA, Biacore™ assay or a competition assay.

Bait expression can be inhibited by any of several acceptable means. For example, the polynucleotides encoding the bait can be expressed by a regulatable promoter whose expression can be inhibited in the host cell. In an embodiment of the invention, bait expression is inhibited by RNA interference, anti-sense RNA, mutation or removal of the polynucleotide encoding the bait from the host cell or genetic mutation of the polynucleotide so that the host cell does not express a functional bait.

“Acceptable affinity” refers to antibody or antigen-binding fragment affinity for the antigen which is at least about 10⁻³ M or a greater affinity (lower number), e.g., about 10⁻³ M, 10⁻⁴ M, 10⁻⁵ M, 10⁻⁶ M, 10⁻⁷ M, 10⁻⁸ M, 10⁻⁹ M, 10⁻¹⁰ M, 10⁻¹¹ M or 10⁻¹² M.

In an embodiment of the present invention, polynucleotides encoding the free antibody or antigen-binding fragment thereof; or the bait/antigen-binding fragment or bait/antibody heavy and light immunoglobulin chains are in one or more libraries of polynucleotides that encode light and/or heavy chain immunoglobulins (e.g., one library encoding light chains and one library encoding heavy chains). The particular immunoglobulin chains of interest are, in this embodiment, distinguished from the other chains in the library when the surface-anchored bait/antigen-binding fragment or bait/antibody on the host cell surface is observed to bind to an antigen of interest.

In an embodiment of the invention, the heavy or light chain immunoglobulin expressed in the antibody display system is from a library source and the other immunoglobulin chain is known (i.e., a single chain from a clonal source). In this embodiment of the invention, the antibody display system can be used, as discussed herein, to identify a new library chain that forms desirable antibodies or antigen-binding fragments thereof when coupled with the known chain. Alternatively, the antibody display system can be used to analyze expression and binding characteristics of an antibody or antigen-binding fragment thereof comprising two known immunoglobulin chains.

The antibody display system of the present invention may be used to evaluate whether a one or more mutations in an immunoglobulin heavy chain (e.g., the Fc region of the immunoglobulin heavy chain, e.g., in the CH2 and/or CH3 domain of the heavy chain) agonizes or antagonizes binding of the heavy chain to an Fc receptor (e.g., FcγRI (CD64), FcγRIIA (CD32), FcγRIIB (CD32), FcγRIIIA (CD16a), FcγRIIIB (CD16b)) or to a lectin (e.g., DC-SIGN (CD209) and mouse ortholog SIGN-R, DCIR (dendritic cells inhibitory receptor)). For example, in an embodiment of the invention, the method comprise contacting an antibody display system with said Fc receptor or lectin; wherein the antibody display system comprises: (a) an isolated eukaryotic host cell comprising a polynucleotide encoding an immunoglobulin light chain; and a polynucleotide encoding an immunoglobulin heavy chain which comprises the mutation(s) to be evaluated; and (b) a bait comprising a light chain immunoglobulin or functional fragment thereof fused to a surface anchor polypeptide or functional fragment thereof on the surface of said eukaryotic host cell; wherein the light chain immunoglobulin of said bait complexes with a heavy chain immunoglobulin, to form a bait/antigen-binding fragment or bait/antibody, on the surface of the host cell; determining if said bait/antigen-binding fragment or bait/antibody specifically binds to said Fc receptor or lectin; determining the binding affinity of the antibody or antigen-binding fragment thereof for the Fc receptor or lectin; and comparing the affinity of the antibody or antigen-binding fragment thereof with affinity of an otherwise identical antibody or antigen-binding fragment thereof which lacks said mutation; wherein the mutation is determined to increase affinity for the Fc receptor or lectin (agonize binding) if the affinity of the antibody or antigen-binding fragment thereof comprising said mutation is higher than the affinity of the antibody or antigen-binding fragment thereof which lacks the mutation, and/or wherein the mutation is determined to decrease affinity for the Fc receptor or lectin (antagonize binding) if the affinity of antibody or antigen-binding fragment thereof comprising said mutation is lower than the affinity of the antibody or antigen-binding fragment thereof which lacks the mutation. For example, the affinity of the antibody or antigen-binding fragment thereof lacking the mutation can be determined in a similar manner in the antibody display system of the present invention or the affinity of it can be determined directly by measuring affinity by a known method such as ELISA, Biacore™ assay or a competition assay. In an embodiment of the invention, the heavy chain immunoglobulin comprising the mutation (e.g., the Fc region of the immunoglobulin heavy chain, e.g., in the CH2 and/or CH3 domain of the heavy chain) is from a library source wherein the clones in the library comprises one or more mutations in the heavy chain (e.g., in the Fc region of the immunoglobulin heavy chain, e.g., in the CH2 and/or CH3 domain of the heavy chain).

In an embodiment of the invention, cells expressing bait/antigen-binding fragment or bait/antibody tethered to the cell by an anchor such as SED1 that bind to an antigen can be detected by incubating the cells with fluorescently labeled antigen (e.g., biotin label) and sorting/selecting cells that specifically bind the antigen by fluorescence-activated cell sorting (FACS). Thus, in an embodiment of the invention, the eukaryotic host cells expressing the bait/antigen-binding fragment or bait/antibody bound with the antigen are identified and sorted using fluorescence-activated cell sorting (FACS). For example, in an embodiment of the invention, cells expressing the bait/antigen-binding fragment or bait/antibody bound to the antigen on the cell surface are labeled with a fluorescent antigen or fluorescent secondary antibody that also binds to the antigen. The fluorescent label is detected during the FACS sorting and used as the signal for sorting. Labeled cells indicate the presence of a cell surface expressed bait/antigen-binding fragment or bait/antibody bound to antigen and are collected in one vessel whereas cells not expressing signal are collected in a separate vessel. The present invention, accordingly, includes a method comprising the following steps for determining if an antibody or antigen-binding fragment thereof from a library specifically binds to an antigen:

-   -   (1) Transform:         -   (i) one or more immunoglobulin libraries, containing             polynucleotides encoding light and heavy chain             immunoglobulins;         -   (ii) one or more immunoglobulin libraries, containing             polynucleotides encoding light chain immunoglobulins and a             single clonal heavy chain immunoglobulin; or         -   (iii) one or more immunoglobulin libraries, containing             polynucleotides encoding heavy chain immunoglobulins and a             single clonal light chain immunoglobulin;         -   wherein, said chains are capable of forming an antibody or             antigen-binding fragment thereof, into a eukaryotic host             cell comprising polynucleotides encoding the bait (e.g.,             Pichia pastoris);     -   (2) Grow transformed cells in a liquid culture medium;     -   (3) Allow expression of the bait on the surface of the cells;     -   (4) Label the cells with fluorescently labeled antigen or         antigen bound to a fluorescently labeled secondary antibody;     -   (5) Sort and isolate fluorescently labeled cells using FACS for         one round;     -   (6) Regrow the labeled, sorted cells;     -   (7) Allow expression of the bait in the cells;     -   (8) Label the cells with fluorescently labeled antigen or         antigen bound to a fluorescently labeled secondary antibody;     -   (9) Sort and isolate fluorescently labeled cells using FACS for         a second round;     -   (10) Regrow the labeled, sorted cells on solid culture medium so         that individual cellular clones grow into discrete cellular         colonies;     -   (11) Identify colonies with affinity for the antigen;     -   (12) Grow cells from identified colonies in a liquid culture         medium and isolate supernatant containing full, non-tethered         antibody or antigen-binding fragment thereof comprising the         immunoglobulin light and heavy chains; wherein, expression of         the bait is optionally inhibited;     -   (13) Determine affinity of non-tethered antibodies or         antigen-binding fragments thereof, from the supernatant, for the         antigen and identify clones with acceptable affinity (e.g., by         Biacore™ analysis);     -   (14) Determine the nucleotide sequence of polynucleotides in the         identified clones encoding the heavy and light chain         immunoglobulins.

The scope of the present invention also includes a method for identifying polynucleotides encoding a heavy chain and light chain immunoglobulin of an antibody or antigen-binding fragment thereof or for identifying an antibody or antigen-binding fragment thereof which exhibits high stability. Such a method comprises the following steps:

(a) co-expressing the bait and the polynucleotides encoding the heavy and light chains in a eukaryotic host cell (e.g., Pichia pastoris) while subjecting antibodies comprising said chains to a denaturant;

In an embodiment of the invention, a denaturant is present in a concentration or amount or magnitude (e.g., at a sufficiently high temperature) that a practitioner of ordinary skill in the art would expect to, at least partially, denature an antibody and, thus, inhibit its ability to bind to an antigen. For example, possible denaturants include urea (e.g., 2, 3, 4, 5 or 6 M or more), detergent such as triton X-100 (e.g., 1% or more), dithiothreitol (DTT) (e.g., 250 mM or 500 mM or more), guanidine hydrochloride, light (e.g., ultraviolet or visible), extreme pH (e.g., 1, 2, 3, 14, 13 or 12) or a temperature above about 4° C., such as 37° C. (e.g., 42° C., 48° C. or 50° C.) or any combination thereof (e.g., 500 mM DTT/6 M urea).

(b) identifying a eukaryotic host cell expressing bait/antigen-binding fragment or bait/antibody that has detectable affinity (e.g., acceptable affinity) for the antigen;

In an embodiment of the invention, full antibodies comprising light and heavy chain variable regions identical to those complexed with the bait are also analyzed to determine if they possess detectable affinity.

In an embodiment of the invention, the full antibodies are secreted from the host cell. In an embodiment of the invention, the full antibodies are isolated from the host cell.

In an embodiment of the invention, expression of the bait in the host cell is inhibited, but expression of the full antibodies is not inhibited. In this embodiment of the invention, the host cell expresses only the full antibody but does not express the bait at any significant quantity. Once expression of the bait is inhibited, in an embodiment of the invention, the full antibody produced from the host cell is analyzed to determine if it possesses detectable affinity (e.g., acceptable affinity); and,

(c) identifying said antibodies or polynucleotides encoding the heavy and light chains from the cell wherein one or more of the polynucleotides are optionally isolated from the host cell; wherein antibodies exhibiting affinity for the antigen in the presence of denaturant are determined to exhibit high stability. In an embodiment of the invention, the nucleotide sequence of the polynucleotide is determined.

In an embodiment of the invention, sed1p is Saccharomyces cerevisiae sed1p which, in an embodiment of the invention, comprises the following amino acid sequence: (SEQ ID NO:1)

VDQFSNSTSASSTDVTSSSSISTSSGSVTITSSEAPESDNGTSTAAPTET STEAPTTAIPTNGTSTEAPTTAIPTNGTSTEAPTDTTTEAPTTALPTNGT STEAPTDTTTEAPTTGLPTNGTTSAFPPTTSLPPSNTTTTPPYNPSTDYT TDYTVVTEYTTYCPEPTTFTTNGKTYTVTEPTTLTITDCPCTIEKPTTTS TTEYTVVTEYTTYCPEPTTFTTNGKTYTVTEPTTLTITDCPCTIEKSEAP ESSVPVTESKGTTTKETGVTTKQTTANPSLTVSTVVPVSSSASSHSVVIN SNGANVVVPGALGLAGVAMLFL. The corresponding nucleotide sequence (SED-1) encoding sed1p is (SEQ ID NO:2):

CAATTCTCTAACTCTACTTCCGCTTCCTCTACTGACGTTACTTCCTCCTC CTCTATTTCTACTTCCTCCGGTTCCGTTACTATTACTTCCTCTGAGGCTC CAGAATCTGACAACGGTACTTCTACTGCTGCTCCAACTGAAACTTCTACT GAGGCTCCTACTACTGCTATTCCAACTAACGGAACTTCCACAGAGGCTCC AACAACAGCTATCCCTACAAACGGTACATCCACTGAAGCTCCTACTGACA CTACTACAGAAGCTCCAACTACTGCTTTGCCTACTAATGGTACATCAACA GAGGCTCCTACAGATACAACAACTGAAGCTCCAACAACTGGATTGCCAAC AAACGGTACTACTTCTGCTTTCCCACCAACTACTTCCTTGCCACCATCCA ACACTACTACTACTCCACCATACAACCCATCCACTGACTACACTACTGAC TACACAGTTGTTACTGAGTACACTACTTACTGTCCAGAGCCAACTACTTT CACAACAAACGGAAAGACTTACACTGTTACTGAGCCTACTACTTTGACTA TCACTGACTGTCCATGTACTATCGAGAAGCCAACTACTACTTCCACTACA GAGTATACTGTTGTTACAGAATACACAACATATTGTCCTGAGCCAACAAC ATTCACTACTAATGGAAAAACATACACAGTTACAGAACCAACTACATTGA CAATTACAGATTGTCCTTGTACAATTGAGAAGTCCGAGGCTCCTGAATCT TCTGTTCCAGTTACTGAATCCAAGGGTACTACTACTAAAGAAACTGGTGT TACTACTAAGCAGACTACTGCTAACCCATCCTTGACTGTTTCCACTGTTG TTCCAGTTTCTTCCTCTGCTTCTTCCCACTCCGTTGTTATCAACTCCAAC GGTGCTAACGTTGTTGTTCCTGGTGCTTTGGGATTGGCTGGTGTTGCTAT GTTGTTCTTG

In an embodiment of the invention, the bait is linked to a signal sequence such as an alpha mating factor signal sequence of Saccharomyces cerevisiae (e.g., MRFPSIFTAVLFAASSALA (SEQ ID NO: 3)), encoded by nucleotide sequence SEQ ID NO:4:

ATGAGATTCCCATCCATCTTCACTGCTGTTTTGTTCGCTGCTTCCTCTGC TTTGGCT.

In an embodiment of the invention, the bait comprising the human light chain immunoglobulin domain fused to a Sed1p polypeptide comprises the amino acid sequence (SEQ ID NO: 5) with the light chain immunoglobulin domain underlined and the linker is in bold, followed by the Sed1p sequence:

DIQMTQSPSSLSASVGDRVTITCKASQNVGTNVVWYQQKPGKAPKALIHS ASYRYSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQYKTYPYTFGQ GTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKV DNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQG LSSPVTKSFNRGEC GGGGSGGGGSGGGGSVDQFSNSTSASSTDVTSSSSI STSSGSVTITSSEAPESDNGTSTAAPTETSTEAPTTAIPTNGTSTEAPTT AIPTNGTSTEAPTDTTTEAPTTALPTNGTSTEAPTDTTTEAPTTGLPTNG TTSAFPPTTSLPPSNTTTTPPYNPSTDYTTDYTVVTEYTTYCPEPTTFTT NGKTYTVTEPTTLTITDCPCTIEKPTTTSTTEYTVVTEYTTYCPEPTTFT TNGKTYTVTEPTTLTITDCPCTIEKSEAPESSVPVTESKGTTTKETGVTT KQTTANPSLTVSTVVPVSSSASSHSVVINSNGANVVVPGALGLAGVAMLF L The corresponding nucleotide sequence encoding SEQ ID NO: 5 is SEQ ID NO:6 (with light chain sequence underlined, the linker sequence in bold, followed by the SED-1 sequence in plain text):

GACATTCAAATGACTCAGTCCCCATCTTCCTTGTCTGCTTCCGTTGGTGA CAGAGTTACTATCACTTGTAAGGCTTCCCAGAACGTTGGAACTAACGTTG TTTGGTATCAGCAGAAGCCAGGTAAGGCTCCAAAGGCTTTGATTCACTCC GCTTCATACAGATACTCCGGTGTTCCATCCAGATTCTCTGGTTCTGGTTC CGGTACTGACTTTACTTTGACTATCTCCTCATTGCAGCCAGAGGACTTCG CTACTTACTACTGTCAGCAGTACAAGACTTACCCATACACTTTCGGTCAG GGTACCAAGGTTGAGATCAAGAGAACTGTTGCTGCTCCATCCGTTTTCAT TTTCCCACCATCCGACGAACAGTTGAAGTCTGGTACAGCTTCCGTTGTTT GTTTGTTGAACAACTTCTACCCAAGAGAGGCTAAGGTTCAGTGGAAGGTT GACAACGCTTTGCAATCCGGTAACTCCCAAGAATCCGTTACTGAGCAAGA CTCTAAGGACTCCACTTACTCCTTGTCCTCCACTTTGACTTTGTCCAAGG CTGATTACGAGAAGCACAAGGTTTACGCTTGTGAGGTTACACATCAGGGT TTGTCCTCCCCAGTTACTAAGTCCTTCAACAGAGGAGAGTGT GGTGGTGG TGGTTCCGGTGGTGGTGGTTCTGGTGGTGGTGGTTCTCAATTCTCTAACT CTACTTCCGCTTCCTCTACTGACGTTACTTCCTCCTCCTCTATTTCTACT TCCTCCGGTTCCGTTACTATTACTTCCTCTGAGGCTCCAGAATCTGACAA CGGTACTTCTACTGCTGCTCCAACTGAAACTTCTACTGAGGCTCCTACTA CTGCTATTCCAACTAACGGAACTTCCACAGAGGCTCCAACAACAGCTATC CCTACAAACGGTACATCCACTGAAGCTCCTACTGACACTACTACAGAAGC TCCAACTACTGCTTTGCCTACTAATGGTACATCAACAGAGGCTCCTACAG ATACAACAACTGAAGCTCCAACAACTGGATTGCCAACAAACGGTACTACT TCTGCTTTCCCACCAACTACTTCCTTGCCACCATCCAACACTACTACTAC TCCACCATACAACCCATCCACTGACTACACTACTGACTACACAGTTGTTA CTGAGTACACTACTTACTGTCCAGAGCCAACTACTTTCACAACAAACGGA AAGACTTACACTGTTACTGAGCCTACTACTTTGACTATCACTGACTGTCC ATGTACTATCGAGAAGCCAACTACTACTTCCACTACAGAGTATACTGTTG TTACAGAATACACAACATATTGTCCTGAGCCAACAACATTCACTACTAAT GGAAAAACATACACAGTTACAGAACCAACTACATTGACAATTACAGATTG TCCTTGTACAATTGAGAAGTCCGAGGCTCCTGAATCTTCTGTTCCAGTTA CTGAATCCAAGGGTACTACTACTAAAGAAACTGGTGTTACTACTAAGCAG ACTACTGCTAACCCATCCTTGACTGTTTCCACTGTTGTTCCAGTTTCTTC CTCTGCTTCTTCCCACTCCGTTGTTATCAACTCCAACGGTGCTAACGTTG TTGTTCCTGGTGCTTTGGGATTGGCTGGTGTTGCTATGTTGTTCTTG

EXAMPLES

The present invention is intended to exemplify the present invention and not to be a limitation thereof. The methods and compositions (e.g., polypeptides, polynucleotides, plasmids, yeast cells) disclosed below fall within the scope of the present invention.

Example 1 Construction of Expression Cassettes

A polynucleotide encoding the N-terminus of a cell surface anchoring protein S. cerevisiae Sed1p that inherently contains an attached glycophosphotidylinositol (GPI) post-translational modification that anchors the protein on the yeast cell wall was linked to a nucleic acid sequence that encodes the human IgG2 anti PCSK9 (1F11) Light Chain (Lc).

The plasmid pGLY11714 containing anti-PCSK9 Lc bait cassette was constructed using a codon optimized sequence of human IgG2 Lc (VL+CL) fragment, which was synthesized and fused in frame to the 3′ end of the nucleic acid sequence of S. cerevisiae α-mating factor signal sequence. The nucleic acid sequence of three of the (GGGS, SEQ ID NO:10) linker was used to link the nucleic acid sequence of Lc 3′ end to the 5′ end of S. cerevisiae Sed1p. The construct was subcloned into pGLY9008 at EcoRI-SalI (replacing the Fc) by the contracting research organization (CRO) Genewiz. As in the above example, the resulting plasmid enables delivery of the Lc-SED1 cassette under the control of the Pichia pastoris AOX1 promoter at the URA6 locus in Pichia pastoris.

Nucleic Acid Sequence of pGLY11714 (SEQ ID NO: 7)

TCGCGCGTTTCGGTGATGACGGTGAAAACCTCTGACACATGCAGCTCCCG GAGACGGTCACAGCTTGTCTGTAAGCGGATGCCGGGAGCAGACAAGCCCG TCAGGGCGCGTCAGCGGGTGTTGGCGGGTGTCGGGGCTGGCTTAACTATG CGGCATCAGAGCAGATTGTACTGAGAGTGCACCATATGCGGTGTGAAATA CCGCACAGATGCGTAAGGAGAAAATACCGCATCAGGCGCCATTCGCCATT CAGGCTGCGCAACTGTTGGGAAGGGCGATCGGTGCGGGCCTCTTCGCTAT TACGCCAGCTGGCGAAAGGGGGATGTGCTGCAAGGCGATTAAGTTGGGTA ACGCCAGGGTTTTCCCAGTCACGACGTTGTAAAACGACGGCCAGTGAATT GAGATCTAACATCCAAAGACGAAAGGTTGAATGAAACCTTTTTGCCATCC GACATCCACAGGTCCATTCTCACACATAAGTGCCAAACGCAACAGGAGGG GATACACTAGCAGCAGACCGTTGCAAACGCAGGACCTCCACTCCTCTTCT CCTCAACACCCACTTTTGCCATCGAAAAACCAGCCCAGTTATTGGGCTTG ATTGGAGCTCGCTCATTCCAATTCCTTCTATTAGGCTACTAACACCATGA CTTTATTAGCCTGTCTATCCTGGCCCCCCTGGCGAGGTTCATGTTTGTTT ATTTCCGAATGCAACAAGCTCCGCATTACACCCGAACATCACTCCAGATG AGGGCTTTCTGAGTGTGGGGTCAAATAGTTTCATGTTCCCCAAATGGCCC AAAACTGACAGTTTAAACGCTGTCTTGGAACCTAATATGACAAAAGCGTG ATCTCATCCAAGATGAACTAAGTTTGGTTCGTTGAAATGCTAACGGCCAG TTGGTCAAAAAGAAACTTCCAAAAGTCGGCATACCGTTTGTCTTGTTTGG TATTGATTGACGAATGCTCAAAAATAATCTCATTAATGCTTAGCGCAGTC TCTCTATCGCTTCTGAACCCCGGTGCACCTGTGCCGAAACGCAAATGGGG AAACACCCGCTTTTTGGATGATTATGCATTGTCTCCACATTGTATGCTTC CAAGATTCTGGTGGGAATACTGCTGATAGCCTAACGTTCATGATCAAAAT TTAACTGTTCTAACCCCTACTTGACAGCAATATATAAACAGAAGGAAGCT GCCCTGTCTTAAACCTTTTTTTTTATCATCATTATTAGCTTACTTTCATA ATTGCGACTGGTTCCAATTGACAAGCTTTTGATTTTAACGACTTTTAACG ACAACTTGAGAAGATCAAAAAACAACTAATTATTCGAAACGGAATTCACG ATGAGATTCCCATCCATCTTCACTGCTGTTTTGTTCGCTGCTTCCTCTGC TTTGGCTGACATTCAAATGACTCAGTCCCCATCTTCCTTGTCTGCTTCCG TTGGTGACAGAGTTACTATCACTTGTAAGGCTTCCCAGAACGTTGGAACT AACGTTGTTTGGTATCAGCAGAAGCCAGGTAAGGCTCCAAAGGCTTTGAT TCACTCCGCTTCATACAGATACTCCGGTGTTCCATCCAGATTCTCTGGTT CTGGTTCCGGTACTGACTTTACTTTGACTATCTCCTCATTGCAGCCAGAG GACTTCGCTACTTACTACTGTCAGCAGTACAAGACTTACCCATACACTTT CGGTCAGGGTACCAAGGTTGAGATCAAGAGAACTGTTGCTGCTCCATCCG TTTTCATTTTCCCACCATCCGACGAACAGTTGAAGTCTGGTACAGCTTCC GTTGTTTGTTTGTTGAACAACTTCTACCCAAGAGAGGCTAAGGTTCAGTG GAAGGTTGACAACGCTTTGCAATCCGGTAACTCCCAAGAATCCGTTACTG AGCAAGACTCTAAGGACTCCACTTACTCCTTGTCCTCCACTTTGACTTTG TCCAAGGCTGATTACGAGAAGCACAAGGTTTACGCTTGTGAGGTTACACA TCAGGGTTTGTCCTCCCCAGTTACTAAGTCCTTCAACAGAGGAGAGTGTG GTGGTGGTGGTTCCGGTGGTGGTGGTTCTGGTGGTGGTGGTTCTGTCGAC CAATTCTCTAACTCTACTTCCGCTTCCTCTACTGACGTTACTTCCTCCTC CTCTATTTCTACTTCCTCCGGTTCCGTTACTATTACTTCCTCTGAGGCTC CAGAATCTGACAACGGTACTTCTACTGCTGCTCCAACTGAAACTTCTACT GAGGCTCCTACTACTGCTATTCCAACTAACGGAACTTCCACAGAGGCTCC AACAACAGCTATCCCTACAAACGGTACATCCACTGAAGCTCCTACTGACA CTACTACAGAAGCTCCAACTACTGCTTTGCCTACTAATGGTACATCAACA GAGGCTCCTACAGATACAACAACTGAAGCTCCAACAACTGGATTGCCAAC AAACGGTACTACTTCTGCTTTCCCACCAACTACTTCCTTGCCACCATCCA ACACTACTACTACTCCACCATACAACCCATCCACTGACTACACTACTGAC TACACAGTTGTTACTGAGTACACTACTTACTGTCCAGAGCCAACTACTTT CACAACAAACGGAAAGACTTACACTGTTACTGAGCCTACTACTTTGACTA TCACTGACTGTCCATGTACTATCGAGAAGCCAACTACTACTTCCACTACA GAGTATACTGTTGTTACAGAATACACAACATATTGTCCTGAGCCAACAAC ATTCACTACTAATGGAAAAACATACACAGTTACAGAACCAACTACATTGA CAATTACAGATTGTCCTTGTACAATTGAGAAGTCCGAGGCTCCTGAATCT TCTGTTCCAGTTACTGAATCCAAGGGTACTACTACTAAAGAAACTGGTGT TACTACTAAGCAGACTACTGCTAACCCATCCTTGACTGTTTCCACTGTTG TTCCAGTTTCTTCCTCTGCTTCTTCCCACTCCGTTGTTATCAACTCCAAC GGTGCTAACGTTGTTGTTCCTGGTGCTTTGGGATTGGCTGGTGTTGCTAT GTTGTTCTTGTAATAGGGCCGGCCATTTAAATACAGGCCCCTTTTCCTTT GTCGATATCATGTAATTAGTTATGTCACGCTTACATTCACGCCCTCCTCC CACATCCGCTCTAACCGAAAAGGAAGGAGTTAGACAACCTGAAGTCTAGG TCCCTATTTATTTTTTTTAATAGTTATGTTAGTATTAAGAACGTTATTTA TATTTCAAATTTTTCTTTTTTTTCTGTACAAACGCGTGTACGCATGTAAC ATTATACTGAAAACCTTGCTTGAGAAGGTTTTGGGACGCTCGAAGGCTTT AATTTGCAAGCTGGATCCGCGGCCGCTTACGCGCCGTTCTTCGCTTGGTC TTGTATCTCCTTACACTGTATCTTCCCATTTGCGTTTAGGTGGTTATCAA AAACTAAAAGGAAAAATTTCAGATGTTTATCTCTAAGGTTTTTTCTTTTT ACAGTATAACACGTGATGCGTCACGTGGTACTAGATTACGTAAGTTATTT TGGTCCGGTGGGTAAGTGGGTAAGAATAGAAAGCATGAAGGTTTACAAAA ACGCAGTCACGAATTATTGCTACTTCGAGCTTGGAACCACCCCAAAGATT ATATTGTACTGATGCACTACCTTCTCGATTTTGCTCCTCCAAGAACCTAC GAAAAACATTTCTTGAGCCTTTTCAACCTAGACTACACATCAAGTTATTT AAGGTATGTTCCGTTAACATGTAAGAAAAGGAGAGGATAGATCGTTTATG GGGTACGTCGCCTGATTCAAGCGTGACCATTCGAAGAATAGGCCTTCGAA AGCTGAATAAAGCAAATGTCAGTTGCGATTGGTATGCTGACAAATTAGCA TAAAAAGCAATAGACTTTCTAACCACCTGTTTTTTTCCTTTTACTTTATT TATATTTTGCCACCGTACTAACAAGTTCAGACAAATTAATTAACACCATG TCAGAAGATCAAAAAAGTGAAAATTCCGTACCTTCTAAGGTTAATATGGT GAATCGCACCGATATACTGACTACGATCAAGTCATTGTCATGGCTTGACT TGATGTTGCCATTTACTATAATTCTCTCCATAATCATTGCAGTAATAATT TCTGTCTATGTGCCTTCTTCCCGTCACACTTTTGACGCTGAAGGTCATCC CAATCTAATGGGAGTGTCCATTCCTTTGACTGTTGGTATGATTGTAATGA TGATTCCCCCGATCTGCAAAGTTTCCTGGGAGTCTATTCACAAGTACTTC TACAGGAGCTATATAAGGAAGCAACTAGCCCTCTCGTTATTTTTGAATTG GGTCATCGGTCCTTTGTTGATGACAGCATTGGCGTGGATGGCGCTATTCG ATTATAAGGAATACCGTCAAGGCATTATTATGATCGGAGTAGCTAGATGC ATTGCCATGGTGCTAATTTGGAATCAGATTGCTGGAGGAGACAATGATCT CTGCGTCGTGCTTGTTATTACAAACTCGCTTTTACAGATGGTATTATATG CACCATTGCAGATATTTTACTGTTATGTTATTTCTCATGACCACCTGAAT ACTTCAAATAGGGTATTATTCGAAGAGGTTGCAAAGTCTGTCGGAGTTTT TCTCGGCATACCACTGGGAATTGGCATTATCATACGTTTGGGAAGTCTTA CCATAGCTGGTAAAAGTAATTATGAAAAATACATTTTGAGATTTATTTCT CCATGGGCAATGATCGGATTTCATTACACTTTATTTGTTATTTTTATTAG TAGAGGTTATCAATTTATCCACGAAATTGGTTCTGCAATATTGTGCTTTG TCCCATTGGTGCTTTACTTCTTTATTGCATGGTTTTTGACCTTCGCATTA ATGAGGTACTTATCAATATCTAGGAGTGATACACAAAGAGAATGTAGCTG TGACCAAGAACTACTTTTAAAGAGGGTCTGGGGAAGAAAGTCTTGTGAAG CTAGCTTTTCTATTACGATGACGCAATGTTTCACTATGGCTTCAAATAAT TTTGAACTATCCCTGGCAATTGCTATTTCCTTATATGGTAACAATAGCAA GCAAGCAATAGCTGCAACATTTGGGCCGTTGCTAGAAGTTCCAATTTTAT TGATTTTGGCAATAGTCGCGAGAATCCTTAAACCATATTATATATGGAAC AATAGAAATTAATTAACAGGCCCCTTTTCCTTTGTCGATATCATGTAATT AGTTATGTCACGCTTACATTCACGCCCTCCTCCCACATCCGCTCTAACCG AAAAGGAAGGAGTTAGACAACCTGAAGTCTAGGTCCCTATTTATTTTTTT TAATAGTTATGTTAGTATTAAGAACGTTATTTATATTTCAAATTTTTCTT TTTTTTCTGTACAAACGCGTGTACGCATGTAACATTATACTGAAAACCTT GCTTGAGAAGGTTTTGGGACGCTCGAAGGCTTTAATTTGCAAGCTGCGGC CTAAGGCGCGCCAGGCCATAATGGCCCAAATGCAAGAGGACATTAGAAAT GTGTTTGGTAAGAACATGAAGCCGGAGGCATACAAACGATTCACAGATTT GAAGGAGGAAAACAAACTGCATCCACCGGAAGTGCCAGCAGCCGTGTATG CCAACCTTGCTCTCAAAGGCATTCCTACGGATCTGAGTGGGAAATATCTG AGATTCACAGACCCACTATTGGAACAGTACCAAACCTAGTTTGGCCGATC CATGATTATGTAATGCATATAGTTTTTGTCGATGCTCACCCGTTTCGAGT CTGTCTCGTATCGTCTTACGTATAAGTTCAAGCATGTTTACCAGGTCTGT TAGAAACTCCTTTGTGAGGGCAGGACCTATTCGTCTCGGTCCCGTTGTTT CTAAGAGACTGTACAGCCAAGCGCAGAATGGTGGCATTAACCATAAGAGG ATTCTGATCGGACTTGGTCTATTGGCTATTGGAACCACCCTTTACGGGAC AACCAACCCTACCAAGACTCCTATTGCATTTGTGGAACCAGCCACGGAAA GAGCGTTTAAGGACGGAGACGTCTCTGTGATTTTTGTTCTCGGAGGTCCA GGAGCTGGAAAAGGTACCCAATGTGCCAAACTAGTGAGTAATTACGGATT TGTTCACCTGTCAGCTGGAGACTTGTTACGTGCAGAACAGAAGAGGGAGG GGTCTAAGTATGGAGAGATGATTTCCCAGTATATCAGAGATGGACTGATA GTACCTCAAGAGGTCACCATTGCGCTCTTGGAGCAGGCCATGAAGGAAAA CTTCGAGAAAGGGAAGACACGGTTCTTGATTGATGGATTCCCTCGTAAGA TGGACCAGGCCAAAACTTTTGAGGAAAAAGTCGCAAAGTCCAAGGTGACA CTTTTCTTTGATTGTCCCGAATCAGTGCTCCTTGAGAGATTACTTAAAAG AGGACAGACAAGCGGAAGAGAGGATGATAATGCGGAGAGTATCAAAAAAA GATTCAAAACATTCGTGGAAACTTCGATGCCTGTGGTGGACTATTTCGGG AAGCAAGGACGCGTTTTGAAGGTATCTTGTGACCACCCTGTGGATCAAGT GTATTCACAGGTTGTGTCGGTGCTAAAAGAGAAGGGGATCTTTGCCGATA ACGAGACGGAGAATAAATAAACATTGTAATAAGATTTAGACTGTGAATGT TCTATGTAATATTTTTCGAGATACTGTATCTATCTGGTGTACCGTATCAC TCTGGACTTGCAAACTCATTGATTACTTGTGCAATGGGCAAGAAGGATAG CTCTAGAAAGAAGAAGAAAAAGGAGCCGCCTGAAGAGCTGGATCTTTCCG AGGTTGTTCCAACTTTTGGTTATGAGGAATTTCATGTTGAGCAAGAGGAG AATCCGGTCGATCAAGACGAACTTGACGGCCATAATGGCCTAGCTTGGCG TAATCATGGTCATAGCTGTTTCCTGTGTGAAATTGTTATCCGCTCACAAT TCCACACAACATACGAGCCGGAAGCATAAAGTGTAAAGCCTGGGGTGCCT AATGAGTGAGCTAACTCACATTAATTGCGTTGCGCTCACTGCCCGCTTTC CAGTCGGGAAACCTGTCGTGCCAGCTGCATTAATGAATCGGCCAACGCGC GGGGAGAGGCGGTTTGCGTATTGGGCGCTCTTCCGCTTCCTCGCTCACTG ACTCGCTGCGCTCGGTCGTTCGGCTGCGGCGAGCGGTATCAGCTCACTCA AAGGCGGTAATACGGTTATCCACAGAATCAGGGGATAACGCAGGAAAGAA CATGTGAGCAAAAGGCCAGCAAAAGGCCAGGAACCGTAAAAAGGCCGCGT TGCTGGCGTTTTTCCATAGGCTCCGCCCCCCTGACGAGCATCACAAAAAT CGACGCTCAAGTCAGAGGTGGCGAAACCCGACAGGACTATAAAGATACCA GGCGTTTCCCCCTGGAAGCTCCCTCGTGCGCTCTCCTGTTCCGACCCTGC CGCTTACCGGATACCTGTCCGCCTTTCTCCCTTCGGGAAGCGTGGCGCTT TCTCATAGCTCACGCTGTAGGTATCTCAGTTCGGTGTAGGTCGTTCGCTC CAAGCTGGGCTGTGTGCACGAACCCCCCGTTCAGCCCGACCGCTGCGCCT TATCCGGTAACTATCGTCTTGAGTCCAACCCGGTAAGACACGACTTATCG CCACTGGCAGCAGCCACTGGTAACAGGATTAGCAGAGCGAGGTATGTAGG CGGTGCTACAGAGTTCTTGAAGTGGTGGCCTAACTACGGCTACACTAGAA GGACAGTATTTGGTATCTGCGCTCTGCTGAAGCCAGTTACCTTCGGAAAA AGAGTTGGTAGCTCTTGATCCGGCAAACAAACCACCGCTGGTAGCGGTGG TTTTTTTGTTTGCAAGCAGCAGATTACGCGCAGAAAAAAAGGATCTCAAG AAGATCCTTTGATCTTTTCTACGGGGTCTGACGCTCAGTGGAACGAAAAC TCACGTTAAGGGATTTTGGTCATGAGATTATCAAAAAGGATCTTCACCTA GATCCTTTTAAATTAAAAATGAAGTTTTAAATCAATCTAAAGTATATATG AGTAAACTTGGTCTGACAGTTACCAATGCTTAATCAGTGAGGCACCTATC TCAGCGATCTGTCTATTTCGTTCATCCATAGTTGCCTGACTCCCCGTCGT GTAGATAACTACGATACGGGAGGGCTTACCATCTGGCCCCAGTGCTGCAA TGATACCGCGAGACCCACGCTCACCGGCTCCAGATTTATCAGCAATAAAC CAGCCAGCCGGAAGGGCCGAGCGCAGAAGTGGTCCTGCAACTTTATCCGC CTCCATCCAGTCTATTAATTGTTGCCGGGAAGCTAGAGTAAGTAGTTCGC CAGTTAATAGTTTGCGCAACGTTGTTGCCATTGCTACAGGCATCGTGGTG TCACGCTCGTCGTTTGGTATGGCTTCATTCAGCTCCGGTTCCCAACGATC AAGGCGAGTTACATGATCCCCCATGTTGTGCAAAAAAGCGGTTAGCTCCT TCGGTCCTCCGATCGTTGTCAGAAGTAAGTTGGCCGCAGTGTTATCACTC ATGGTTATGGCAGCACTGCATAATTCTCTTACTGTCATGCCATCCGTAAG ATGCTTTTCTGTGACTGGTGAGTACTCAACCAAGTCATTCTGAGAATAGT GTATGCGGCGACCGAGTTGCTCTTGCCCGGCGTCAATACGGGATAATACC GCGCCACATAGCAGAACTTTAAAAGTGCTCATCATTGGAAAACGTTCTTC GGGGCGAAAACTCTCAAGGATCTTACCGCTGTTGAGATCCAGTTCGATGT AACCCACTCGTGCACCCAACTGATCTTCAGCATCTTTTACTTTCACCAGC GTTTCTGGGTGAGCAAAAACAGGAAGGCAAAATGCCGCAAAAAAGGGAAT AAGGGCGACACGGAAATGTTGAATACTCATACTCTTCCTTTTTCAATATT ATTGAAGCATTTATCAGGGTTATTGTCTCATGAGCGGATACATATTTGAA TGTATTTAGAAAAATAAACAAATAGGGGTTCCGCGCACATTTCCCCGAAA AGTGCCACCTGACGTCTAAGAAACCATTATTATCATGACATTAACCTATA AAAATAGGCGTATCACGAGGCCCTTTCGTC Amino Acid Sequence of Anti-PCSK9 Light Chain (SEQ ID NO:8)

DIQMTQSPSSLSASVGDRVTITCKASQNVGTNVVWYQQKPGKAPKALIHS ASYRYSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQYKTYPYTFGQ GTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKV DNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQG LSSPVTKSFNRGEC Amino Acid Sequence of Alpha Mating Factor-antipPCSK9 Lc-(GGGS, SEQ ID NO:10) Linker-S. cerevisiae Sed1p (SEQ ID NO:9)

MRFPSIFTAVLFAASSALADIQMTQSPSSLSASVGDRVTITCKASQNVGT NVVWYQQKPGKAPKALIHSASYRYSGVPSRFSGSGSGTDFTLTISSLQPE DFATYYCQQYKTYPYTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTAS VVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTL SKADYEKHKVYACEVTHQGLSSPVTKSFNRGECGGGGSGGGGSGGGGSVD QFSNSTSASSTDVTSSSSISTSSGSVTITSSEAPESDNGTSTAAPTETST EAPTTAIPTNGTSTEAPTTAIPTNGTSTEAPTDTTTEAPTTALPTNGTST EAPTDTTTEAPTTGLPTNGTTSAFPPTTSLPPSNTTTTPPYNPSTDYTTD YTVVTEYTTYCPEPTTFTTNGKTYTVTEPTTLTITDCPCTIEKPTTTSTT EYTVVTEYTTYCPEPTTFTTNGKTYTVTEPTTLTITDCPCTIEKSEAPES SVPVTESKGTTTKETGVTTKQTTANPSLTVSTVVPVSSSASSHSVVINSN GANVVVPGALGLAGVAMLFL

Example 2 Glycoengineered Monoclonal Antibody Production Strains

To test this system for displaying full length antibodies (comprising human IgGs) on the yeast cell wall, pGLY11714 was introduced into Pichia pastoris strains that were previously selected and created as expression hosts of human anti-Her2 or anti-PCSK9 IgGs (as described in PCT/US2011/62286). An empty Pichia pastoris strain was included as a control. Different IgG forms (IgG1, IgG2 and IgG4) were included in this study to establish the ability to capture the different antibody forms.

TABLE 1 Strains Used Strain Anti-body IgG form YGLY8316 Null Null YGLY13979 Anti-Her2 Human IgG1 YGLY21352 Anti-PCSK9 Human IgG2 YGLY23236 Anti-PCSK9 Human IgG4 YGLY22982 Anti-PCSK9 Human IgG2(F243A/V264A) Sialylated YGLY25266 Anti-PCSK9 Human IgG2(F243A/V264A/S267E/L328F) Sialylated

The glycoengineered Pichia pastoris monoclonal antibody production strains in Table 1 were grown in 50 mL BMGY media until the culture optical density, at 600 nm, was 2. The cells were washed three times with 1 M sorbitol and resuspended in 1 mL 1 M sorbitol. About 1-2 micrograms of SpeI linearized pGLY11714 was mixed with these competent cells. Transformation was performed with a BioRad electroporation apparatus using the manufacturer's program specific for electroporation of nucleic acids into Pichia pastoris. One milliliter of recovery media was added to the cells, which were then plated out on yeast-soytone-dextrose (YSD) media with 50 μg/mL arsenite.

Example 3 Growth and Induction of Lc-Sed1p Displaying Yeast

By detecting the Fc fragment on the cell surface, it could be established that antibodies could be displayed using the Lc-Sed1p system, since the only way for the Fc to be displayed on cell surface is through heterodimerization of both the light chain to the heavy chain. To this end glycoengineered yeast expressing human IgGs and the Lc-SED1 bait expression cassette were inoculated using 600 μL BMGY in a 96 deep well plate or 50 mL BMGY in a 250 mL shake flasks for two days. The cells were collected by centrifugation and the supernatant was discarded. The cells were induced by incubation in 300 μL or 25 mL BMMY with PMTi inhibitor overnight following the methods described in International Patent Application Publication No. WO2007/061631.

Example 4 Flow Cytometry Detection of Surface Displayed Antibodies

To determine the efficiency of surface displaying antibodies using this method, cells were labeled with APC 635 labeled mouse anti-Human Fc, which detects the Fc fragment of human antibody molecules, and were processed by flow cytometry. Briefly, each culture, after growth to an optical density of 2 at 600 nm was pelleted by centrifugation and washed in 100 μL PBS. Cells were incubated for 30 minutes at room temperature (RT) in 100 μL phosphate buffer saline (PBS) containing fluorescently labeled (APC635) mouse anti-human Fc and washed in 100 μl PBS. One hundred microliters of PBS was used to resuspend pellets before analyzing in a flow cytometer. (See FIGS. 3A-D).

Flow cytometry analysis was conducted using the cells co-expressing Lc-Sed1p bait and anti-Her2 (FIG. 3B), or Lc-Sed1p bait and anti-PCSK9 variants (FIGS. 3C and D). Control was prepared in which an empty strain expressing full length anti-Her2 antibody (H2+L2) only (FIG. 3A) or a strain that expressed the Lc-Sed1p. Strains co-expressing anti-Her2 with the Lc-Sed1p bait (FIG. 3B), or anti-PCSK9 with the Lc-Sed1p bait (FIG. 3C) were found to display significant levels of anti-Fc binding while strains lacking the Lc-Sed1p bait showed background signal levels (FIG. 3A), thus suggesting that Lc-Sed1p bait captured the heavy chain fragment containing the Fc. In FIGS. 3A-D the fluorescent intensities from these experiments were compared. FIG. 3B shows the different fluorescence intensities for anti-Her2 displaying cells while FIG. 3C shows the intensities for the anti-PCSK9 displaying cells, and the parent strains that did not contain the Lc-Sed1p bait (FIG. 3A).

Example 5 Illustration of Display Format for Modulating Binding to Fc Receptors

The display format of the present invention facilitates engineering of the Fc fragment to enable modulating binding to Fc receptors. The binding of Fc receptors to the different displayed IgGs was tested to illustrate this principle. Human Fc gamma Receptor I and Human Fc gamma Receptor IIb were used since they have different affinities to different Fc forms. Mouse Fc gamma Receptor IIb was used as a control. 100 nM of each receptor (His tagged R and D Systems) was incubated at RT for 30 min with a 600 nm optical density of 2 of each culture as described earlier in 100 μL phosphate buffer saline then washed in 100 μl of same buffer. One microliter of FITC conjugated anti-His fragment was added to cells in 100 microliters of PBS and incubated at RT for 15 min. Cells were pelleted washed in 100 microliter PBS and resuspended in 100 microliter PBS before analyzing in a flow cytometric system.

As shown in FIG. 3A, cells from the strain expressing the full length antibody without the Lc-Sed1 system did not stain with anti-His FITC while strains expressing IgGs along with the Lc-Sed1p reacted with anti-His FITC regardless of antibody, IgG type, or glycoform indicating all Fc forms were able to bind Fc gamma Receptor I. These results illustrate that the light and heavy chains were fully assembled on the cell surface.

In contrast, only strains containing the four mutations (F243A/V264A/S267E/L328F) in Fc reacted with anti-His FITC suggesting that Fc form was able to bind Fc gamma Receptor IIb (FIG. 3D). This is in agreement with Biacore data obtained from soluble IgGs. This shows that this method can be used to engineer Fc fragments with desirable Fc gamma receptor binding for enhancement of biological and pharmacokinetic properties.

The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, the scope of the present invention includes embodiments specifically set forth herein and other embodiments not specifically set forth herein; the embodiments specifically set forth herein are not necessarily intended to be exhaustive. Various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the claims.

Patents, patent applications, publications, product descriptions, and protocols are cited throughout this application, the disclosures of which are incorporated herein by reference in their entireties for all purposes. 

We claim:
 1. An antibody display system comprising: (a) an isolated host cell, wherein the host cell is a Pichia or Saccharomyces cerevisiae cell; (b) a bait comprising a full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof fused to a signal peptide, wherein the bait polypeptide is located on the extracellular cell membrane surface of the host cell; (c) one or more polynucleotides encoding a full-length immunoglobulin light chain; (d) one or more polynucleotides encoding a full-length immunoglobulin heavy chain; (e) a full-length monovalent antibody comprising two said full-length immunoglobulin heavy chains and two full-length immunoglobulin light chains, wherein the full-length antibody is tethered to the extracellular cell membrane surface of the host cell via the first full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof, wherein the second full-length light chain immunoglobulin chain and both full-length heavy chain immunoglobulin chains are not fused to a surface anchor polypeptide or functional fragment thereof, wherein the second full-length light chain immunoglobulin chain and both full-length heavy chain immunoglobulin chains are encoded by said polynucleotides; and (f) a secreted full-length monovalent antibody comprising two said full-length immunoglobulin heavy chains and two said full-length immunoglobulin light chains encoded by said polynucleotides.
 2. The antibody display system of claim 1, wherein said one or more polynucleotides encoding an immunoglobulin light chain is from a genetically diverse population of immunoglobulin light chains; and/or, wherein said one or more polynucleotides encoding an immunoglobulin heavy chain is from a genetically diverse population of immunoglobulin heavy chains.
 3. The antibody display system of claim 1, wherein the host cell comprises a polynucleotide encoding the bait which is operably associated with a regulatable promoter.
 4. A method for determining if a full-length antibody, secreted from a host cell, specifically binds to an antigen comprising contacting an antibody display system with said antigen; wherein the antibody display system comprises: (a) an isolated host cell, wherein the host cell is a Pichia or Saccharomyces cerevisiae cell; (b) a bait comprising a full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof fused to a signal peptide, wherein the bait polypeptide is located on the extracellular cell membrane surface of the host cell; (c) one or more polynucleotides encoding a full-length immunoglobulin light chain; (d) one or more polynucleotides encoding a full-length immunoglobulin heavy chain; (e) a full-length monovalent antibody comprising two said full-length immunoglobulin heavy chains and two full-length immunoglobulin light chains, wherein the full-length antibody is tethered to the extracellular cell membrane surface of the host cell via the first full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof, wherein the second full-length light chain immunoglobulin chain and both full-length heavy chain immunoglobulin chains are not fused to a surface anchor polypeptide or functional fragment thereof, wherein the second full-length light chain immunoglobulin chain and both full-length heavy chain immunoglobulin chains are encoded by said polynucleotides; and (f) a secreted full-length monovalent antibody comprising two said full-length immunoglobulin heavy chains and two said full-length immunoglobulin light chains encoded by said polynucleotides; and determining if a bait/full-length antibody comprising said bait and heavy and light chain immunoglobulins specifically binds, at the cell surface, to said antigen; wherein the secreted full-length antibody is determined to specifically bind said antigen if said bait/full-length antibody specifically binds, at the cell surface, to said antigen.
 5. The method of claim 4 further comprising isolating the identified polynucleotides.
 6. The method of claim 4 further comprising inhibiting expression of said bait, and determining the affinity of said secreted antibody or antigen-binding fragment thereof for said antigen.
 7. The method of claim 4 further comprising recombinantly expressing the immunoglobulin chains encoded by the polynucleotides and, optionally, isolating an antibody or antigen-binding fragment thereof comprising said immunoglobulins and, optionally, producing a pharmaceutical formulation comprising combining said antibody or antigen-binding fragment thereof and a pharmaceutically acceptable carrier.
 8. A method for making the antibody display system of claim 1, comprising: (a) providing an isolated eukaryotic host cell, wherein the host cell is a Pichia or Saccharomyces cerevisiae cell, (b) introducing, into said host cell a bait comprising a full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof fused to a signal peptide, wherein the bait polypeptide is located on the extracellular cell membrane surface of the host cell; and (i) one or more polynucleotides encoding a full-length immunoglobulin light chain; and (ii) one or more polynucleotides encoding a full-length immunoglobulin heavy chain.
 9. A method for making a full-length antibody comprising: (a) providing an isolated eukaryotic host cell, wherein the host cell is a Pichia or Saccharomyces cerevisiae cell, (b) introducing, into said host cell a bait comprising a full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof fused to a signal peptide, wherein the bait polypeptide is located on the extracellular cell membrane surface of the host cell; and (i) one or more polynucleotides encoding a full-length immunoglobulin light chain; and (ii) one or more polynucleotides encoding a full-length immunoglobulin heavy chain; and culturing the host cell under condition whereby the polynucleotides encoding the immunoglobulin chains are expressed and an antibody or antigen-binding fragment thereof is formed from said chains; wherein said bait is operably associated with a regulatable promoter and bait expression is inhibited when said immunoglobulin chains are expressed.
 10. A method for determining the effect of a sugar on a full-length antibody which specifically binds to an antigen comprising contacting an antibody display system with said antigen; wherein the antibody display system comprises: (a) an isolated host cell, wherein the host cell is a Pichia or Saccharomyces cerevisiae cell; (b) a bait comprising a full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof fused to a signal peptide, wherein the bait polypeptide is located on the extracellular cell membrane surface of the host cell; (c) one or more polynucleotides encoding a full-length immunoglobulin light chain; (d) one or more polynucleotides encoding a full-length immunoglobulin heavy chain; (e) a full-length monovalent antibody comprising two said full-length immunoglobulin heavy chains and two full-length immunoglobulin light chains, wherein the full-length antibody is tethered to the extracellular cell membrane surface of the host cell via the first full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof, wherein the second full-length light chain immunoglobulin chain and both full-length heavy chain immunoglobulin chains are not fused to a surface anchor polypeptide or functional fragment thereof, wherein the second full-length light chain immunoglobulin chain and both full-length heavy chain immunoglobulin chains are encoded by said polynucleotides; and (f) a secreted full-length monovalent antibody comprising two said full-length immunoglobulin heavy chains and two said full-length immunoglobulin light chains encoded by said polynucleotides; wherein said heavy or light chain comprises said sugar; determining if said bait/full-length antibody specifically binds to said antigen; determining the binding affinity of the full-length antibody comprising said sugar for the antigen; and comparing the affinity of the full-length antibody with affinity of an otherwise identical full-length antibody which lacks said sugar; wherein the sugar is determined to increase affinity for the antigen if the affinity of the full-length antibody comprising said sugar is higher than the affinity of the full-length antibody which lacks the sugar, and/or wherein the sugar is determined to decrease affinity for the antigen if the affinity of the full-length antibody comprising said sugar is lower than the affinity of the full-length antibody which lacks the sugar.
 11. A method for determining the whether an mutation in an immunoglobulin heavy chain Fc region increases or decreases binding of said chain to an Fc receptor or to a lectin comprising contacting an antibody display system with said Fc receptor or lectin; wherein the antibody display system comprises: (a) an isolated host cell, wherein the host cell is a Pichia or Saccharomyces cerevisiae cell; (b) a bait comprising a full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof fused to a signal peptide, wherein the bait polypeptide is located on the extracellular cell membrane surface of the host cell; (c) one or more polynucleotides encoding a full-length immunoglobulin light chain; (d) one or more polynucleotides encoding a full-length immunoglobulin heavy chain; (e) a full-length monovalent antibody comprising two said full-length immunoglobulin heavy chains and two full-length immunoglobulin light chains, wherein the full-length antibody is tethered to the extracellular cell membrane surface of the host cell via the first full-length light immunoglobulin chain fused to a surface anchor polypeptide or functional fragment thereof, wherein the second full-length light chain immunoglobulin chain and both full-length heavy chain immunoglobulin chains are not fused to a surface anchor polypeptide or functional fragment thereof, wherein the second full-length light chain immunoglobulin chain and both full-length heavy chain immunoglobulin chains are encoded by said polynucleotides; and (f) a secreted full-length monovalent antibody comprising two said full-length immunoglobulin heavy chains and two said full-length immunoglobulin light chains encoded by said polynucleotides; and determining if said bait/full-length antibody specifically binds to said Fc receptor or lectin; and determining the binding affinity of the full-length antibody for the Fc receptor or lectin; and comparing the affinity of the full-length antibody with affinity of an otherwise identical full-length antibody which lacks said mutation; wherein the mutation is determined to increase affinity of the heavy chain for the Fc receptor or lectin if the affinity of the full-length antibody comprising said mutation is higher than the affinity of the full-length antibody which lacks the mutation, and/or wherein the mutation is determined to decrease affinity for the Fc receptor or lectin if the affinity of full-length antibody comprising said mutation is lower than the affinity of the full-length antibody which lacks the mutation. 